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How do I include a JavaScript file inside another JavaScript file, similar to #import in CSS?
The old versions of JavaScript had no import, include, or require, so many different approaches to this problem have been developed.
But since 2015 (ES6), JavaScript has had the ES6 modules standard to import modules in Node.js, which is also supported by most modern browsers.
For compatibility with older browsers, build tools like Webpack and Rollup and/or transpilation tools like Babel can be used.
ES6 Modules
ECMAScript (ES6) modules have been supported in Node.js since v8.5, with the --experimental-modules flag, and since at least Node.js v13.8.0 without the flag. To enable "ESM" (vs. Node.js's previous CommonJS-style module system ["CJS"]) you either use "type": "module" in package.json or give the files the extension .mjs. (Similarly, modules written with Node.js's previous CJS module can be named .cjs if your default is ESM.)
Using package.json:
{
"type": "module"
}
Then module.js:
export function hello() {
return "Hello";
}
Then main.js:
import { hello } from './module.js';
let val = hello(); // val is "Hello";
Using .mjs, you'd have module.mjs:
export function hello() {
return "Hello";
}
Then main.mjs:
import { hello } from './module.mjs';
let val = hello(); // val is "Hello";
ECMAScript modules in browsers
Browsers have had support for loading ECMAScript modules directly (no tools like Webpack required) since Safari 10.1, Chrome 61, Firefox 60, and Edge 16. Check the current support at caniuse. There is no need to use Node.js' .mjs extension; browsers completely ignore file extensions on modules/scripts.
<script type="module">
import { hello } from './hello.mjs'; // Or the extension could be just `.js`
hello('world');
</script>
// hello.mjs -- or the extension could be just `.js`
export function hello(text) {
const div = document.createElement('div');
div.textContent = `Hello ${text}`;
document.body.appendChild(div);
}
Read more at https://jakearchibald.com/2017/es-modules-in-browsers/
Dynamic imports in browsers
Dynamic imports let the script load other scripts as needed:
<script type="module">
import('hello.mjs').then(module => {
module.hello('world');
});
</script>
Read more at https://developers.google.com/web/updates/2017/11/dynamic-import
Node.js require
The older CJS module style, still widely used in Node.js, is the module.exports/require system.
// mymodule.js
module.exports = {
hello: function() {
return "Hello";
}
}
// server.js
const myModule = require('./mymodule');
let val = myModule.hello(); // val is "Hello"
There are other ways for JavaScript to include external JavaScript contents in browsers that do not require preprocessing.
AJAX Loading
You could load an additional script with an AJAX call and then use eval to run it. This is the most straightforward way, but it is limited to your domain because of the JavaScript sandbox security model. Using eval also opens the door to bugs, hacks and security issues.
Fetch Loading
Like Dynamic Imports you can load one or many scripts with a fetch call using promises to control order of execution for script dependencies using the Fetch Inject library:
fetchInject([
'https://cdn.jsdelivr.net/momentjs/2.17.1/moment.min.js'
]).then(() => {
console.log(`Finish in less than ${moment().endOf('year').fromNow(true)}`)
})
jQuery Loading
The jQuery library provides loading functionality in one line:
$.getScript("my_lovely_script.js", function() {
alert("Script loaded but not necessarily executed.");
});
Dynamic Script Loading
You could add a script tag with the script URL into the HTML. To avoid the overhead of jQuery, this is an ideal solution.
The script can even reside on a different server. Furthermore, the browser evaluates the code. The <script> tag can be injected into either the web page <head>, or inserted just before the closing </body> tag.
Here is an example of how this could work:
function dynamicallyLoadScript(url) {
var script = document.createElement("script"); // create a script DOM node
script.src = url; // set its src to the provided URL
document.head.appendChild(script); // add it to the end of the head section of the page (could change 'head' to 'body' to add it to the end of the body section instead)
}
This function will add a new <script> tag to the end of the head section of the page, where the src attribute is set to the URL which is given to the function as the first parameter.
Both of these solutions are discussed and illustrated in JavaScript Madness: Dynamic Script Loading.
Detecting when the script has been executed
Now, there is a big issue you must know about. Doing that implies that you remotely load the code. Modern web browsers will load the file and keep executing your current script because they load everything asynchronously to improve performance. (This applies to both the jQuery method and the manual dynamic script loading method.)
It means that if you use these tricks directly, you won't be able to use your newly loaded code the next line after you asked it to be loaded, because it will be still loading.
For example: my_lovely_script.js contains MySuperObject:
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
var s = new MySuperObject();
Error : MySuperObject is undefined
Then you reload the page hitting F5. And it works! Confusing...
So what to do about it ?
Well, you can use the hack the author suggests in the link I gave you. In summary, for people in a hurry, he uses an event to run a callback function when the script is loaded. So you can put all the code using the remote library in the callback function. For example:
function loadScript(url, callback)
{
// Adding the script tag to the head as suggested before
var head = document.head;
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = url;
// Then bind the event to the callback function.
// There are several events for cross browser compatibility.
script.onreadystatechange = callback;
script.onload = callback;
// Fire the loading
head.appendChild(script);
}
Then you write the code you want to use AFTER the script is loaded in a lambda function:
var myPrettyCode = function() {
// Here, do whatever you want
};
Then you run all that:
loadScript("my_lovely_script.js", myPrettyCode);
Note that the script may execute after the DOM has loaded, or before, depending on the browser and whether you included the line script.async = false;. There's a great article on Javascript loading in general which discusses this.
Source Code Merge/Preprocessing
As mentioned at the top of this answer, many developers use build/transpilation tool(s) like Parcel, Webpack, or Babel in their projects, allowing them to use upcoming JavaScript syntax, provide backward compatibility for older browsers, combine files, minify, perform code splitting etc.
If anyone is looking for something more advanced, try out RequireJS. You'll get added benefits such as dependency management, better concurrency, and avoid duplication (that is, retrieving a script more than once).
You can write your JavaScript files in "modules" and then reference them as dependencies in other scripts. Or you can use RequireJS as a simple "go get this script" solution.
Example:
Define dependencies as modules:
some-dependency.js
define(['lib/dependency1', 'lib/dependency2'], function (d1, d2) {
//Your actual script goes here.
//The dependent scripts will be fetched if necessary.
return libraryObject; //For example, jQuery object
});
implementation.js is your "main" JavaScript file that depends on some-dependency.js
require(['some-dependency'], function(dependency) {
//Your script goes here
//some-dependency.js is fetched.
//Then your script is executed
});
Excerpt from the GitHub README:
RequireJS loads plain JavaScript files as well as more defined
modules. It is optimized for in-browser use, including in a Web
Worker, but it can be used in other JavaScript environments, like
Rhino and Node. It implements the Asynchronous Module API.
RequireJS uses plain script tags to load modules/files, so it should
allow for easy debugging. It can be used simply to load existing
JavaScript files, so you can add it to your existing project without
having to re-write your JavaScript files.
...
There actually is a way to load a JavaScript file not asynchronously, so you could use the functions included in your newly loaded file right after loading it, and I think it works in all browsers.
You need to use jQuery.append() on the <head> element of your page, that is:
$("head").append($("<script></script>").attr("src", url));
/* Note that following line of code is incorrect because it doesn't escape the
* HTML attribute src correctly and will fail if `url` contains special characters:
* $("head").append('<script src="' + url + '"></script>');
*/
However, this method also has a problem: if an error happens in the imported JavaScript file, Firebug (and also Firefox Error Console and Chrome Developer Tools as well) will report its place incorrectly, which is a big problem if you use Firebug to track JavaScript errors down a lot (I do). Firebug simply doesn't know about the newly loaded file for some reason, so if an error occurs in that file, it reports that it occurred in your main HTML file, and you will have trouble finding out the real reason for the error.
But if that is not a problem for you, then this method should work.
I have actually written a jQuery plugin called $.import_js() which uses this method:
(function($)
{
/*
* $.import_js() helper (for JavaScript importing within JavaScript code).
*/
var import_js_imported = [];
$.extend(true,
{
import_js : function(script)
{
var found = false;
for (var i = 0; i < import_js_imported.length; i++)
if (import_js_imported[i] == script) {
found = true;
break;
}
if (found == false) {
$("head").append($('<script></script').attr('src', script));
import_js_imported.push(script);
}
}
});
})(jQuery);
So all you would need to do to import JavaScript is:
$.import_js('/path_to_project/scripts/somefunctions.js');
I also made a simple test for this at Example.
It includes a main.js file in the main HTML and then the script in main.js uses $.import_js() to import an additional file called included.js, which defines this function:
function hello()
{
alert("Hello world!");
}
And right after including included.js, the hello() function is called, and you get the alert.
(This answer is in response to e-satis' comment).
Another way, that in my opinion is much cleaner, is to make a synchronous Ajax request instead of using a <script> tag. Which is also how Node.js handles includes.
Here's an example using jQuery:
function require(script) {
$.ajax({
url: script,
dataType: "script",
async: false, // <-- This is the key
success: function () {
// all good...
},
error: function () {
throw new Error("Could not load script " + script);
}
});
}
You can then use it in your code as you'd usually use an include:
require("/scripts/subscript.js");
And be able to call a function from the required script in the next line:
subscript.doSomethingCool();
It is possible to dynamically generate a JavaScript tag and append it to HTML document from inside other JavaScript code. This will load targeted JavaScript file.
function includeJs(jsFilePath) {
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
}
includeJs("/path/to/some/file.js");
There is a good news for you. Very soon you will be able to load JavaScript code easily. It will become a standard way of importing modules of JavaScript code and will be part of core JavaScript itself.
You simply have to write import cond from 'cond.js'; to load a macro named cond from a file cond.js.
So you don't have to rely upon any JavaScript framework nor do you have to explicitly make Ajax calls.
Refer to:
Static module resolution
Module loaders
Statement import is in ECMAScript 6.
Syntax
import name from "module-name";
import { member } from "module-name";
import { member as alias } from "module-name";
import { member1 , member2 } from "module-name";
import { member1 , member2 as alias2 , [...] } from "module-name";
import name , { member [ , [...] ] } from "module-name";
import "module-name" as name;
Maybe you can use this function that I found on this page How do I include a JavaScript file in a JavaScript file?:
function include(filename)
{
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.src = filename;
script.type = 'text/javascript';
head.appendChild(script)
}
Here is a synchronous version without jQuery:
function myRequire( url ) {
var ajax = new XMLHttpRequest();
ajax.open( 'GET', url, false ); // <-- the 'false' makes it synchronous
ajax.onreadystatechange = function () {
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4) {
switch( ajax.status) {
case 200:
eval.apply( window, [script] );
console.log("script loaded: ", url);
break;
default:
console.log("ERROR: script not loaded: ", url);
}
}
};
ajax.send(null);
}
Note that to get this working cross-domain, the server will need to set allow-origin header in its response.
I just wrote this JavaScript code (using Prototype for DOM manipulation):
var require = (function() {
var _required = {};
return (function(url, callback) {
if (typeof url == 'object') {
// We've (hopefully) got an array: time to chain!
if (url.length > 1) {
// Load the nth file as soon as everything up to the
// n-1th one is done.
require(url.slice(0, url.length - 1), function() {
require(url[url.length - 1], callback);
});
} else if (url.length == 1) {
require(url[0], callback);
}
return;
}
if (typeof _required[url] == 'undefined') {
// Haven't loaded this URL yet; gogogo!
_required[url] = [];
var script = new Element('script', {
src: url,
type: 'text/javascript'
});
script.observe('load', function() {
console.log("script " + url + " loaded.");
_required[url].each(function(cb) {
cb.call(); // TODO: does this execute in the right context?
});
_required[url] = true;
});
$$('head')[0].insert(script);
} else if (typeof _required[url] == 'boolean') {
// We already loaded the thing, so go ahead.
if (callback) {
callback.call();
}
return;
}
if (callback) {
_required[url].push(callback);
}
});
})();
Usage:
<script src="prototype.js"></script>
<script src="require.js"></script>
<script>
require(['foo.js','bar.js'], function () {
/* Use foo.js and bar.js here */
});
</script>
Gist: http://gist.github.com/284442.
If you want it in pure JavaScript, you can use document.write.
document.write('<script src="myscript.js" type="text/javascript"></script>');
If you use the jQuery library, you can use the $.getScript method.
$.getScript("another_script.js");
Here's the generalized version of how Facebook does it for their ubiquitous Like button:
<script>
var firstScript = document.getElementsByTagName('script')[0],
js = document.createElement('script');
js.src = 'https://cdnjs.cloudflare.com/ajax/libs/Snowstorm/20131208/snowstorm-min.js';
js.onload = function () {
// do stuff with your dynamically loaded script
snowStorm.snowColor = '#99ccff';
};
firstScript.parentNode.insertBefore(js, firstScript);
</script>
If it works for Facebook, it will work for you.
The reason why we look for the first script element instead of head or body is because some browsers don't create one if missing, but we're guaranteed to have a script element - this one. Read more at http://www.jspatterns.com/the-ridiculous-case-of-adding-a-script-element/.
You can also assemble your scripts using PHP:
File main.js.php:
<?php
header('Content-type:text/javascript; charset=utf-8');
include_once("foo.js.php");
include_once("bar.js.php");
?>
// Main JavaScript code goes here
Most of solutions shown here imply dynamical loading. I was searching instead for a compiler which assemble all the depended files into a single output file. The same as Less/Sass preprocessors deal with the CSS #import at-rule. Since I didn't find anything decent of this sort, I wrote a simple tool solving the issue.
So here is the compiler, https://github.com/dsheiko/jsic, which replaces $import("file-path") with the requested file content securely. Here is the corresponding Grunt plugin: https://github.com/dsheiko/grunt-jsic.
On the jQuery master branch, they simply concatenate atomic source files into a single one starting with intro.js and ending with outtro.js. That doesn't suits me as it provides no flexibility on the source code design. Check out how it works with jsic:
src/main.js
var foo = $import("./Form/Input/Tel");
src/Form/Input/Tel.js
function() {
return {
prop: "",
method: function(){}
}
}
Now we can run the compiler:
node jsic.js src/main.js build/mail.js
And get the combined file
build/main.js
var foo = function() {
return {
prop: "",
method: function(){}
}
};
If your intention to load the JavaScript file is using the functions from the imported/included file, you can also define a global object and set the functions as object items. For instance:
global.js
A = {};
file1.js
A.func1 = function() {
console.log("func1");
}
file2.js
A.func2 = function() {
console.log("func2");
}
main.js
A.func1();
A.func2();
You just need to be careful when you are including scripts in an HTML file. The order should be as in below:
<head>
<script type="text/javascript" src="global.js"></script>
<script type="text/javascript" src="file1.js"></script>
<script type="text/javascript" src="file2.js"></script>
<script type="text/javascript" src="main.js"></script>
</head>
This should do:
xhr = new XMLHttpRequest();
xhr.open("GET", "/soap/ajax/11.0/connection.js", false);
xhr.send();
eval(xhr.responseText);
Or rather than including at run time, use a script to concatenate prior to upload.
I use Sprockets (I don't know if there are others). You build your JavaScript code in separate files and include comments that are processed by the Sprockets engine as includes. For development you can include files sequentially, then for production to merge them...
See also:
Introducing Sprockets: JavaScript dependency management and concatenation
I had a simple issue, but I was baffled by responses to this question.
I had to use a variable (myVar1) defined in one JavaScript file (myvariables.js) in another JavaScript file (main.js).
For this I did as below:
Loaded the JavaScript code in the HTML file, in the correct order, myvariables.js first, then main.js:
<html>
<body onload="bodyReady();" >
<script src="myvariables.js" > </script>
<script src="main.js" > </script>
<!-- Some other code -->
</body>
</html>
File: myvariables.js
var myVar1 = "I am variable from myvariables.js";
File: main.js
// ...
function bodyReady() {
// ...
alert (myVar1); // This shows "I am variable from myvariables.js", which I needed
// ...
}
// ...
As you saw, I had use a variable in one JavaScript file in another JavaScript file, but I didn't need to include one in another. I just needed to ensure that the first JavaScript file loaded before the second JavaScript file, and, the first JavaScript file's variables are accessible in the second JavaScript file, automatically.
This saved my day. I hope this helps.
In a modern language with the check if script has already been loaded, it would be:
function loadJs( url ){
return new Promise(( resolve, reject ) => {
if (document.querySelector( `head > script[ src = "${url}" ]`) !== null ){
console.warn( `script already loaded: ${url}` );
resolve();
}
const script = document.createElement( "script" );
script.src = url;
script.onload = resolve;
script.onerror = function( reason ){
// This can be useful for your error-handling code
reason.message = `error trying to load script ${url}`;
reject( reason );
};
document.head.appendChild( script );
});
}
Usage (async/await):
try { await loadJs("https://.../script.js"); }
catch(error) { console.log(error); }
or
await loadJs( "https://.../script.js" ).catch( err => {} );
Usage (Promise):
loadJs( "https://.../script.js" ).then( res => {} ).catch( err => {} );
The #import syntax for achieving CSS-like JavaScript importing is possible using a tool such as Mixture via their special .mix file type (see here). I assume the application does this via one of above-mentioned methods.
From the Mixture documentation on .mix files:
Mix files are simply .js or .css files with .mix. in the file name. A
mix file simply extends the functionality of a normal style or
script file and allows you to import and combine.
Here's an example .mix file that combines multiple .js files into one:
// scripts-global.mix.js
// Plugins - Global
#import "global-plugins/headroom.js";
#import "global-plugins/retina-1.1.0.js";
#import "global-plugins/isotope.js";
#import "global-plugins/jquery.fitvids.js";
Mixture outputs this as scripts-global.js and also as a minified version (scripts-global.min.js).
Note: I'm not in any way affiliated with Mixture, other than using it as a front-end development tool. I came across this question upon seeing a .mix JavaScript file in action (in one of the Mixture boilerplates) and being a bit confused by it ("you can do this?" I thought to myself). Then I realized that it was an application-specific file type (somewhat disappointing, agreed). Nevertheless, figured the knowledge might be helpful for others.
Note: Mixture was discontinued on 2016/07/26 (after being open sourced on 2015/04/12).
In case you are using Web Workers and want to include additional scripts in the scope of the worker, the other answers provided about adding scripts to the head tag, etc. will not work for you.
Fortunately, Web Workers have their own importScripts function which is a global function in the scope of the Web Worker, native to the browser itself as it is part of the specification.
Alternatively, as the second highest voted answer to your question highlights, RequireJS can also handle including scripts inside a Web Worker (likely calling importScripts itself, but with a few other useful features).
Although these answers are great, there is a simple "solution" that has been around since script loading existed, and it will cover 99.999% of most people's use cases. Just include the script you need before the script that requires it. For most projects it does not take long to determine which scripts are needed and in what order.
<!DOCTYPE HTML>
<html>
<head>
<script src="script1.js"></script>
<script src="script2.js"></script>
</head>
<body></body>
</html>
If script2 requires script1, this really is the absolute easiest way to do something like this. I'm very surprised no-one has brought this up, as it's the most obvious and simplest answer that will apply in nearly every single case.
ES6 Modules
Yes, use type="module" in a script tag (support):
<script type="module" src="script.js"></script>
And in a script.js file include another file like this:
import { hello } from './module.js';
...
// alert(hello());
In 'module.js' you must export the function/class that you will import:
export function hello() {
return "Hello World";
}
A working example is here.
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
My usual method is:
var require = function (src, cb) {
cb = cb || function () {};
var newScriptTag = document.createElement('script'),
firstScriptTag = document.getElementsByTagName('script')[0];
newScriptTag.src = src;
newScriptTag.async = true;
newScriptTag.onload = newScriptTag.onreadystatechange = function () {
(!this.readyState || this.readyState === 'loaded' || this.readyState === 'complete') && (cb());
};
firstScriptTag.parentNode.insertBefore(newScriptTag, firstScriptTag);
}
It works great and uses no page-reloads for me. I've tried the AJAX method (one of the other answers) but it doesn't seem to work as nicely for me.
Here's an explanation of how the code works for those that are curious: essentially, it creates a new script tag (after the first one) of the URL. It sets it to asynchronous mode so it doesn't block the rest of the code, but calls a callback when the readyState (the state of the content to be loaded) changes to 'loaded'.
I wrote a simple module that automates the job of importing/including module scripts in JavaScript. For detailed explanation of the code, refer to the blog post JavaScript require / import / include modules.
// ----- USAGE -----
require('ivar.util.string');
require('ivar.net.*');
require('ivar/util/array.js');
require('http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js');
ready(function(){
//Do something when required scripts are loaded
});
//--------------------
var _rmod = _rmod || {}; //Require module namespace
_rmod.LOADED = false;
_rmod.on_ready_fn_stack = [];
_rmod.libpath = '';
_rmod.imported = {};
_rmod.loading = {
scripts: {},
length: 0
};
_rmod.findScriptPath = function(script_name) {
var script_elems = document.getElementsByTagName('script');
for (var i = 0; i < script_elems.length; i++) {
if (script_elems[i].src.endsWith(script_name)) {
var href = window.location.href;
href = href.substring(0, href.lastIndexOf('/'));
var url = script_elems[i].src.substring(0, script_elems[i].length - script_name.length);
return url.substring(href.length+1, url.length);
}
}
return '';
};
_rmod.libpath = _rmod.findScriptPath('script.js'); //Path of your main script used to mark
//the root directory of your library, any library.
_rmod.injectScript = function(script_name, uri, callback, prepare) {
if(!prepare)
prepare(script_name, uri);
var script_elem = document.createElement('script');
script_elem.type = 'text/javascript';
script_elem.title = script_name;
script_elem.src = uri;
script_elem.async = true;
script_elem.defer = false;
if(!callback)
script_elem.onload = function() {
callback(script_name, uri);
};
document.getElementsByTagName('head')[0].appendChild(script_elem);
};
_rmod.requirePrepare = function(script_name, uri) {
_rmod.loading.scripts[script_name] = uri;
_rmod.loading.length++;
};
_rmod.requireCallback = function(script_name, uri) {
_rmod.loading.length--;
delete _rmod.loading.scripts[script_name];
_rmod.imported[script_name] = uri;
if(_rmod.loading.length == 0)
_rmod.onReady();
};
_rmod.onReady = function() {
if (!_rmod.LOADED) {
for (var i = 0; i < _rmod.on_ready_fn_stack.length; i++){
_rmod.on_ready_fn_stack[i]();
});
_rmod.LOADED = true;
}
};
_.rmod = namespaceToUri = function(script_name, url) {
var np = script_name.split('.');
if (np.getLast() === '*') {
np.pop();
np.push('_all');
}
if(!url)
url = '';
script_name = np.join('.');
return url + np.join('/')+'.js';
};
//You can rename based on your liking. I chose require, but it
//can be called include or anything else that is easy for you
//to remember or write, except "import", because it is reserved
//for future use.
var require = function(script_name) {
var uri = '';
if (script_name.indexOf('/') > -1) {
uri = script_name;
var lastSlash = uri.lastIndexOf('/');
script_name = uri.substring(lastSlash+1, uri.length);
}
else {
uri = _rmod.namespaceToUri(script_name, ivar._private.libpath);
}
if (!_rmod.loading.scripts.hasOwnProperty(script_name)
&& !_rmod.imported.hasOwnProperty(script_name)) {
_rmod.injectScript(script_name, uri,
_rmod.requireCallback,
_rmod.requirePrepare);
}
};
var ready = function(fn) {
_rmod.on_ready_fn_stack.push(fn);
};
This script will add a JavaScript file to the top of any other <script> tag:
(function () {
var li = document.createElement('script');
li.type = 'text/javascript';
li.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js";
li.async = true;
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(li, s);
})();
Keep it nice, short, simple, and maintainable! :]
// Third-party plugins / script (don't forget the full path is necessary)
var FULL_PATH = '', s =
[
FULL_PATH + 'plugins/script.js' // Script example
FULL_PATH + 'plugins/jquery.1.2.js', // jQuery Library
FULL_PATH + 'plugins/crypto-js/hmac-sha1.js', // CryptoJS
FULL_PATH + 'plugins/crypto-js/enc-base64-min.js' // CryptoJS
];
function load(url)
{
var ajax = new XMLHttpRequest();
ajax.open('GET', url, false);
ajax.onreadystatechange = function ()
{
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4)
{
switch(ajax.status)
{
case 200:
eval.apply( window, [script] );
console.log("library loaded: ", url);
break;
default:
console.log("ERROR: library not loaded: ", url);
}
}
};
ajax.send(null);
}
// Initialize a single load
load('plugins/script.js');
// Initialize a full load of scripts
if (s.length > 0)
{
for (i = 0; i < s.length; i++)
{
load(s[i]);
}
}
This code is simply a short functional example that could require additional feature functionality for full support on any (or given) platform.
I came to this question because I was looking for a simple way to maintain a collection of useful JavaScript plugins. After seeing some of the solutions here, I came up with this:
Set up a file called "plugins.js" (or extensions.js or whatever you want). Keep your plugin files together with that one master file.
plugins.js will have an array called pluginNames[] that we will iterate over each(),
then append a <script> tag to the head for each plugin
//set array to be updated when we add or remove plugin files
var pluginNames = ["lettering", "fittext", "butterjam", etc.];
//one script tag for each plugin
$.each(pluginNames, function(){
$('head').append('<script src="js/plugins/' + this + '.js"></script>');
});
Manually call just the one file in your head:
<script src="js/plugins/plugins.js"></script>
BUT:
Even though all of the plugins get dropped into the head tag the way they ought to, they don't always get run by the browser when you click into the page or refresh.
I've found it's more reliable to just write the script tags in a PHP include. You only have to write it once and that's just as much work as calling the plugin using JavaScript.
There are several ways to implement modules in JavaScript. Here are the two most popular ones:
ES6 Modules
Browsers do not support this moduling system yet, so in order for you to use this syntax you must use a bundler like Webpack. Using a bundler is better anyway because this can combine all of your different files into a single (or a couple of related) files. This will serve the files from the server to the client faster because each HTTP request has some associated overhead accompanied with it. Thus by reducing the overall HTTP request we improve the performance. Here is an example of ES6 modules:
// main.js file
export function add (a, b) {
return a + b;
}
export default function multiply (a, b) {
return a * b;
}
// test.js file
import {add}, multiply from './main'; // For named exports between curly braces {export1, export2}
// For default exports without {}
console.log(multiply(2, 2)); // logs 4
console.log(add(1, 2)); // logs 3
CommonJS (used in Node.js)
This moduling system is used in Node.js. You basically add your exports to an object which is called module.exports. You then can access this object via a require('modulePath'). Important here is to realize that these modules are being cached, so if you require() a certain module twice it will return the already created module.
// main.js file
function add (a, b) {
return a + b;
}
module.exports = add; // Here we add our 'add' function to the exports object
// test.js file
const add = require('./main');
console.log(add(1,2)); // logs 3
How do I include a JavaScript file inside another JavaScript file, similar to #import in CSS?
The old versions of JavaScript had no import, include, or require, so many different approaches to this problem have been developed.
But since 2015 (ES6), JavaScript has had the ES6 modules standard to import modules in Node.js, which is also supported by most modern browsers.
For compatibility with older browsers, build tools like Webpack and Rollup and/or transpilation tools like Babel can be used.
ES6 Modules
ECMAScript (ES6) modules have been supported in Node.js since v8.5, with the --experimental-modules flag, and since at least Node.js v13.8.0 without the flag. To enable "ESM" (vs. Node.js's previous CommonJS-style module system ["CJS"]) you either use "type": "module" in package.json or give the files the extension .mjs. (Similarly, modules written with Node.js's previous CJS module can be named .cjs if your default is ESM.)
Using package.json:
{
"type": "module"
}
Then module.js:
export function hello() {
return "Hello";
}
Then main.js:
import { hello } from './module.js';
let val = hello(); // val is "Hello";
Using .mjs, you'd have module.mjs:
export function hello() {
return "Hello";
}
Then main.mjs:
import { hello } from './module.mjs';
let val = hello(); // val is "Hello";
ECMAScript modules in browsers
Browsers have had support for loading ECMAScript modules directly (no tools like Webpack required) since Safari 10.1, Chrome 61, Firefox 60, and Edge 16. Check the current support at caniuse. There is no need to use Node.js' .mjs extension; browsers completely ignore file extensions on modules/scripts.
<script type="module">
import { hello } from './hello.mjs'; // Or the extension could be just `.js`
hello('world');
</script>
// hello.mjs -- or the extension could be just `.js`
export function hello(text) {
const div = document.createElement('div');
div.textContent = `Hello ${text}`;
document.body.appendChild(div);
}
Read more at https://jakearchibald.com/2017/es-modules-in-browsers/
Dynamic imports in browsers
Dynamic imports let the script load other scripts as needed:
<script type="module">
import('hello.mjs').then(module => {
module.hello('world');
});
</script>
Read more at https://developers.google.com/web/updates/2017/11/dynamic-import
Node.js require
The older CJS module style, still widely used in Node.js, is the module.exports/require system.
// mymodule.js
module.exports = {
hello: function() {
return "Hello";
}
}
// server.js
const myModule = require('./mymodule');
let val = myModule.hello(); // val is "Hello"
There are other ways for JavaScript to include external JavaScript contents in browsers that do not require preprocessing.
AJAX Loading
You could load an additional script with an AJAX call and then use eval to run it. This is the most straightforward way, but it is limited to your domain because of the JavaScript sandbox security model. Using eval also opens the door to bugs, hacks and security issues.
Fetch Loading
Like Dynamic Imports you can load one or many scripts with a fetch call using promises to control order of execution for script dependencies using the Fetch Inject library:
fetchInject([
'https://cdn.jsdelivr.net/momentjs/2.17.1/moment.min.js'
]).then(() => {
console.log(`Finish in less than ${moment().endOf('year').fromNow(true)}`)
})
jQuery Loading
The jQuery library provides loading functionality in one line:
$.getScript("my_lovely_script.js", function() {
alert("Script loaded but not necessarily executed.");
});
Dynamic Script Loading
You could add a script tag with the script URL into the HTML. To avoid the overhead of jQuery, this is an ideal solution.
The script can even reside on a different server. Furthermore, the browser evaluates the code. The <script> tag can be injected into either the web page <head>, or inserted just before the closing </body> tag.
Here is an example of how this could work:
function dynamicallyLoadScript(url) {
var script = document.createElement("script"); // create a script DOM node
script.src = url; // set its src to the provided URL
document.head.appendChild(script); // add it to the end of the head section of the page (could change 'head' to 'body' to add it to the end of the body section instead)
}
This function will add a new <script> tag to the end of the head section of the page, where the src attribute is set to the URL which is given to the function as the first parameter.
Both of these solutions are discussed and illustrated in JavaScript Madness: Dynamic Script Loading.
Detecting when the script has been executed
Now, there is a big issue you must know about. Doing that implies that you remotely load the code. Modern web browsers will load the file and keep executing your current script because they load everything asynchronously to improve performance. (This applies to both the jQuery method and the manual dynamic script loading method.)
It means that if you use these tricks directly, you won't be able to use your newly loaded code the next line after you asked it to be loaded, because it will be still loading.
For example: my_lovely_script.js contains MySuperObject:
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
var s = new MySuperObject();
Error : MySuperObject is undefined
Then you reload the page hitting F5. And it works! Confusing...
So what to do about it ?
Well, you can use the hack the author suggests in the link I gave you. In summary, for people in a hurry, he uses an event to run a callback function when the script is loaded. So you can put all the code using the remote library in the callback function. For example:
function loadScript(url, callback)
{
// Adding the script tag to the head as suggested before
var head = document.head;
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = url;
// Then bind the event to the callback function.
// There are several events for cross browser compatibility.
script.onreadystatechange = callback;
script.onload = callback;
// Fire the loading
head.appendChild(script);
}
Then you write the code you want to use AFTER the script is loaded in a lambda function:
var myPrettyCode = function() {
// Here, do whatever you want
};
Then you run all that:
loadScript("my_lovely_script.js", myPrettyCode);
Note that the script may execute after the DOM has loaded, or before, depending on the browser and whether you included the line script.async = false;. There's a great article on Javascript loading in general which discusses this.
Source Code Merge/Preprocessing
As mentioned at the top of this answer, many developers use build/transpilation tool(s) like Parcel, Webpack, or Babel in their projects, allowing them to use upcoming JavaScript syntax, provide backward compatibility for older browsers, combine files, minify, perform code splitting etc.
If anyone is looking for something more advanced, try out RequireJS. You'll get added benefits such as dependency management, better concurrency, and avoid duplication (that is, retrieving a script more than once).
You can write your JavaScript files in "modules" and then reference them as dependencies in other scripts. Or you can use RequireJS as a simple "go get this script" solution.
Example:
Define dependencies as modules:
some-dependency.js
define(['lib/dependency1', 'lib/dependency2'], function (d1, d2) {
//Your actual script goes here.
//The dependent scripts will be fetched if necessary.
return libraryObject; //For example, jQuery object
});
implementation.js is your "main" JavaScript file that depends on some-dependency.js
require(['some-dependency'], function(dependency) {
//Your script goes here
//some-dependency.js is fetched.
//Then your script is executed
});
Excerpt from the GitHub README:
RequireJS loads plain JavaScript files as well as more defined
modules. It is optimized for in-browser use, including in a Web
Worker, but it can be used in other JavaScript environments, like
Rhino and Node. It implements the Asynchronous Module API.
RequireJS uses plain script tags to load modules/files, so it should
allow for easy debugging. It can be used simply to load existing
JavaScript files, so you can add it to your existing project without
having to re-write your JavaScript files.
...
There actually is a way to load a JavaScript file not asynchronously, so you could use the functions included in your newly loaded file right after loading it, and I think it works in all browsers.
You need to use jQuery.append() on the <head> element of your page, that is:
$("head").append($("<script></script>").attr("src", url));
/* Note that following line of code is incorrect because it doesn't escape the
* HTML attribute src correctly and will fail if `url` contains special characters:
* $("head").append('<script src="' + url + '"></script>');
*/
However, this method also has a problem: if an error happens in the imported JavaScript file, Firebug (and also Firefox Error Console and Chrome Developer Tools as well) will report its place incorrectly, which is a big problem if you use Firebug to track JavaScript errors down a lot (I do). Firebug simply doesn't know about the newly loaded file for some reason, so if an error occurs in that file, it reports that it occurred in your main HTML file, and you will have trouble finding out the real reason for the error.
But if that is not a problem for you, then this method should work.
I have actually written a jQuery plugin called $.import_js() which uses this method:
(function($)
{
/*
* $.import_js() helper (for JavaScript importing within JavaScript code).
*/
var import_js_imported = [];
$.extend(true,
{
import_js : function(script)
{
var found = false;
for (var i = 0; i < import_js_imported.length; i++)
if (import_js_imported[i] == script) {
found = true;
break;
}
if (found == false) {
$("head").append($('<script></script').attr('src', script));
import_js_imported.push(script);
}
}
});
})(jQuery);
So all you would need to do to import JavaScript is:
$.import_js('/path_to_project/scripts/somefunctions.js');
I also made a simple test for this at Example.
It includes a main.js file in the main HTML and then the script in main.js uses $.import_js() to import an additional file called included.js, which defines this function:
function hello()
{
alert("Hello world!");
}
And right after including included.js, the hello() function is called, and you get the alert.
(This answer is in response to e-satis' comment).
Another way, that in my opinion is much cleaner, is to make a synchronous Ajax request instead of using a <script> tag. Which is also how Node.js handles includes.
Here's an example using jQuery:
function require(script) {
$.ajax({
url: script,
dataType: "script",
async: false, // <-- This is the key
success: function () {
// all good...
},
error: function () {
throw new Error("Could not load script " + script);
}
});
}
You can then use it in your code as you'd usually use an include:
require("/scripts/subscript.js");
And be able to call a function from the required script in the next line:
subscript.doSomethingCool();
It is possible to dynamically generate a JavaScript tag and append it to HTML document from inside other JavaScript code. This will load targeted JavaScript file.
function includeJs(jsFilePath) {
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
}
includeJs("/path/to/some/file.js");
There is a good news for you. Very soon you will be able to load JavaScript code easily. It will become a standard way of importing modules of JavaScript code and will be part of core JavaScript itself.
You simply have to write import cond from 'cond.js'; to load a macro named cond from a file cond.js.
So you don't have to rely upon any JavaScript framework nor do you have to explicitly make Ajax calls.
Refer to:
Static module resolution
Module loaders
Statement import is in ECMAScript 6.
Syntax
import name from "module-name";
import { member } from "module-name";
import { member as alias } from "module-name";
import { member1 , member2 } from "module-name";
import { member1 , member2 as alias2 , [...] } from "module-name";
import name , { member [ , [...] ] } from "module-name";
import "module-name" as name;
Maybe you can use this function that I found on this page How do I include a JavaScript file in a JavaScript file?:
function include(filename)
{
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.src = filename;
script.type = 'text/javascript';
head.appendChild(script)
}
Here is a synchronous version without jQuery:
function myRequire( url ) {
var ajax = new XMLHttpRequest();
ajax.open( 'GET', url, false ); // <-- the 'false' makes it synchronous
ajax.onreadystatechange = function () {
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4) {
switch( ajax.status) {
case 200:
eval.apply( window, [script] );
console.log("script loaded: ", url);
break;
default:
console.log("ERROR: script not loaded: ", url);
}
}
};
ajax.send(null);
}
Note that to get this working cross-domain, the server will need to set allow-origin header in its response.
I just wrote this JavaScript code (using Prototype for DOM manipulation):
var require = (function() {
var _required = {};
return (function(url, callback) {
if (typeof url == 'object') {
// We've (hopefully) got an array: time to chain!
if (url.length > 1) {
// Load the nth file as soon as everything up to the
// n-1th one is done.
require(url.slice(0, url.length - 1), function() {
require(url[url.length - 1], callback);
});
} else if (url.length == 1) {
require(url[0], callback);
}
return;
}
if (typeof _required[url] == 'undefined') {
// Haven't loaded this URL yet; gogogo!
_required[url] = [];
var script = new Element('script', {
src: url,
type: 'text/javascript'
});
script.observe('load', function() {
console.log("script " + url + " loaded.");
_required[url].each(function(cb) {
cb.call(); // TODO: does this execute in the right context?
});
_required[url] = true;
});
$$('head')[0].insert(script);
} else if (typeof _required[url] == 'boolean') {
// We already loaded the thing, so go ahead.
if (callback) {
callback.call();
}
return;
}
if (callback) {
_required[url].push(callback);
}
});
})();
Usage:
<script src="prototype.js"></script>
<script src="require.js"></script>
<script>
require(['foo.js','bar.js'], function () {
/* Use foo.js and bar.js here */
});
</script>
Gist: http://gist.github.com/284442.
If you want it in pure JavaScript, you can use document.write.
document.write('<script src="myscript.js" type="text/javascript"></script>');
If you use the jQuery library, you can use the $.getScript method.
$.getScript("another_script.js");
Here's the generalized version of how Facebook does it for their ubiquitous Like button:
<script>
var firstScript = document.getElementsByTagName('script')[0],
js = document.createElement('script');
js.src = 'https://cdnjs.cloudflare.com/ajax/libs/Snowstorm/20131208/snowstorm-min.js';
js.onload = function () {
// do stuff with your dynamically loaded script
snowStorm.snowColor = '#99ccff';
};
firstScript.parentNode.insertBefore(js, firstScript);
</script>
If it works for Facebook, it will work for you.
The reason why we look for the first script element instead of head or body is because some browsers don't create one if missing, but we're guaranteed to have a script element - this one. Read more at http://www.jspatterns.com/the-ridiculous-case-of-adding-a-script-element/.
You can also assemble your scripts using PHP:
File main.js.php:
<?php
header('Content-type:text/javascript; charset=utf-8');
include_once("foo.js.php");
include_once("bar.js.php");
?>
// Main JavaScript code goes here
Most of solutions shown here imply dynamical loading. I was searching instead for a compiler which assemble all the depended files into a single output file. The same as Less/Sass preprocessors deal with the CSS #import at-rule. Since I didn't find anything decent of this sort, I wrote a simple tool solving the issue.
So here is the compiler, https://github.com/dsheiko/jsic, which replaces $import("file-path") with the requested file content securely. Here is the corresponding Grunt plugin: https://github.com/dsheiko/grunt-jsic.
On the jQuery master branch, they simply concatenate atomic source files into a single one starting with intro.js and ending with outtro.js. That doesn't suits me as it provides no flexibility on the source code design. Check out how it works with jsic:
src/main.js
var foo = $import("./Form/Input/Tel");
src/Form/Input/Tel.js
function() {
return {
prop: "",
method: function(){}
}
}
Now we can run the compiler:
node jsic.js src/main.js build/mail.js
And get the combined file
build/main.js
var foo = function() {
return {
prop: "",
method: function(){}
}
};
If your intention to load the JavaScript file is using the functions from the imported/included file, you can also define a global object and set the functions as object items. For instance:
global.js
A = {};
file1.js
A.func1 = function() {
console.log("func1");
}
file2.js
A.func2 = function() {
console.log("func2");
}
main.js
A.func1();
A.func2();
You just need to be careful when you are including scripts in an HTML file. The order should be as in below:
<head>
<script type="text/javascript" src="global.js"></script>
<script type="text/javascript" src="file1.js"></script>
<script type="text/javascript" src="file2.js"></script>
<script type="text/javascript" src="main.js"></script>
</head>
This should do:
xhr = new XMLHttpRequest();
xhr.open("GET", "/soap/ajax/11.0/connection.js", false);
xhr.send();
eval(xhr.responseText);
Or rather than including at run time, use a script to concatenate prior to upload.
I use Sprockets (I don't know if there are others). You build your JavaScript code in separate files and include comments that are processed by the Sprockets engine as includes. For development you can include files sequentially, then for production to merge them...
See also:
Introducing Sprockets: JavaScript dependency management and concatenation
I had a simple issue, but I was baffled by responses to this question.
I had to use a variable (myVar1) defined in one JavaScript file (myvariables.js) in another JavaScript file (main.js).
For this I did as below:
Loaded the JavaScript code in the HTML file, in the correct order, myvariables.js first, then main.js:
<html>
<body onload="bodyReady();" >
<script src="myvariables.js" > </script>
<script src="main.js" > </script>
<!-- Some other code -->
</body>
</html>
File: myvariables.js
var myVar1 = "I am variable from myvariables.js";
File: main.js
// ...
function bodyReady() {
// ...
alert (myVar1); // This shows "I am variable from myvariables.js", which I needed
// ...
}
// ...
As you saw, I had use a variable in one JavaScript file in another JavaScript file, but I didn't need to include one in another. I just needed to ensure that the first JavaScript file loaded before the second JavaScript file, and, the first JavaScript file's variables are accessible in the second JavaScript file, automatically.
This saved my day. I hope this helps.
In a modern language with the check if script has already been loaded, it would be:
function loadJs( url ){
return new Promise(( resolve, reject ) => {
if (document.querySelector( `head > script[ src = "${url}" ]`) !== null ){
console.warn( `script already loaded: ${url}` );
resolve();
}
const script = document.createElement( "script" );
script.src = url;
script.onload = resolve;
script.onerror = function( reason ){
// This can be useful for your error-handling code
reason.message = `error trying to load script ${url}`;
reject( reason );
};
document.head.appendChild( script );
});
}
Usage (async/await):
try { await loadJs("https://.../script.js"); }
catch(error) { console.log(error); }
or
await loadJs( "https://.../script.js" ).catch( err => {} );
Usage (Promise):
loadJs( "https://.../script.js" ).then( res => {} ).catch( err => {} );
The #import syntax for achieving CSS-like JavaScript importing is possible using a tool such as Mixture via their special .mix file type (see here). I assume the application does this via one of above-mentioned methods.
From the Mixture documentation on .mix files:
Mix files are simply .js or .css files with .mix. in the file name. A
mix file simply extends the functionality of a normal style or
script file and allows you to import and combine.
Here's an example .mix file that combines multiple .js files into one:
// scripts-global.mix.js
// Plugins - Global
#import "global-plugins/headroom.js";
#import "global-plugins/retina-1.1.0.js";
#import "global-plugins/isotope.js";
#import "global-plugins/jquery.fitvids.js";
Mixture outputs this as scripts-global.js and also as a minified version (scripts-global.min.js).
Note: I'm not in any way affiliated with Mixture, other than using it as a front-end development tool. I came across this question upon seeing a .mix JavaScript file in action (in one of the Mixture boilerplates) and being a bit confused by it ("you can do this?" I thought to myself). Then I realized that it was an application-specific file type (somewhat disappointing, agreed). Nevertheless, figured the knowledge might be helpful for others.
Note: Mixture was discontinued on 2016/07/26 (after being open sourced on 2015/04/12).
ES6 Modules
Yes, use type="module" in a script tag (support):
<script type="module" src="script.js"></script>
And in a script.js file include another file like this:
import { hello } from './module.js';
...
// alert(hello());
In 'module.js' you must export the function/class that you will import:
export function hello() {
return "Hello World";
}
A working example is here.
In case you are using Web Workers and want to include additional scripts in the scope of the worker, the other answers provided about adding scripts to the head tag, etc. will not work for you.
Fortunately, Web Workers have their own importScripts function which is a global function in the scope of the Web Worker, native to the browser itself as it is part of the specification.
Alternatively, as the second highest voted answer to your question highlights, RequireJS can also handle including scripts inside a Web Worker (likely calling importScripts itself, but with a few other useful features).
Although these answers are great, there is a simple "solution" that has been around since script loading existed, and it will cover 99.999% of most people's use cases. Just include the script you need before the script that requires it. For most projects it does not take long to determine which scripts are needed and in what order.
<!DOCTYPE HTML>
<html>
<head>
<script src="script1.js"></script>
<script src="script2.js"></script>
</head>
<body></body>
</html>
If script2 requires script1, this really is the absolute easiest way to do something like this. I'm very surprised no-one has brought this up, as it's the most obvious and simplest answer that will apply in nearly every single case.
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
My usual method is:
var require = function (src, cb) {
cb = cb || function () {};
var newScriptTag = document.createElement('script'),
firstScriptTag = document.getElementsByTagName('script')[0];
newScriptTag.src = src;
newScriptTag.async = true;
newScriptTag.onload = newScriptTag.onreadystatechange = function () {
(!this.readyState || this.readyState === 'loaded' || this.readyState === 'complete') && (cb());
};
firstScriptTag.parentNode.insertBefore(newScriptTag, firstScriptTag);
}
It works great and uses no page-reloads for me. I've tried the AJAX method (one of the other answers) but it doesn't seem to work as nicely for me.
Here's an explanation of how the code works for those that are curious: essentially, it creates a new script tag (after the first one) of the URL. It sets it to asynchronous mode so it doesn't block the rest of the code, but calls a callback when the readyState (the state of the content to be loaded) changes to 'loaded'.
I wrote a simple module that automates the job of importing/including module scripts in JavaScript. For detailed explanation of the code, refer to the blog post JavaScript require / import / include modules.
// ----- USAGE -----
require('ivar.util.string');
require('ivar.net.*');
require('ivar/util/array.js');
require('http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js');
ready(function(){
//Do something when required scripts are loaded
});
//--------------------
var _rmod = _rmod || {}; //Require module namespace
_rmod.LOADED = false;
_rmod.on_ready_fn_stack = [];
_rmod.libpath = '';
_rmod.imported = {};
_rmod.loading = {
scripts: {},
length: 0
};
_rmod.findScriptPath = function(script_name) {
var script_elems = document.getElementsByTagName('script');
for (var i = 0; i < script_elems.length; i++) {
if (script_elems[i].src.endsWith(script_name)) {
var href = window.location.href;
href = href.substring(0, href.lastIndexOf('/'));
var url = script_elems[i].src.substring(0, script_elems[i].length - script_name.length);
return url.substring(href.length+1, url.length);
}
}
return '';
};
_rmod.libpath = _rmod.findScriptPath('script.js'); //Path of your main script used to mark
//the root directory of your library, any library.
_rmod.injectScript = function(script_name, uri, callback, prepare) {
if(!prepare)
prepare(script_name, uri);
var script_elem = document.createElement('script');
script_elem.type = 'text/javascript';
script_elem.title = script_name;
script_elem.src = uri;
script_elem.async = true;
script_elem.defer = false;
if(!callback)
script_elem.onload = function() {
callback(script_name, uri);
};
document.getElementsByTagName('head')[0].appendChild(script_elem);
};
_rmod.requirePrepare = function(script_name, uri) {
_rmod.loading.scripts[script_name] = uri;
_rmod.loading.length++;
};
_rmod.requireCallback = function(script_name, uri) {
_rmod.loading.length--;
delete _rmod.loading.scripts[script_name];
_rmod.imported[script_name] = uri;
if(_rmod.loading.length == 0)
_rmod.onReady();
};
_rmod.onReady = function() {
if (!_rmod.LOADED) {
for (var i = 0; i < _rmod.on_ready_fn_stack.length; i++){
_rmod.on_ready_fn_stack[i]();
});
_rmod.LOADED = true;
}
};
_.rmod = namespaceToUri = function(script_name, url) {
var np = script_name.split('.');
if (np.getLast() === '*') {
np.pop();
np.push('_all');
}
if(!url)
url = '';
script_name = np.join('.');
return url + np.join('/')+'.js';
};
//You can rename based on your liking. I chose require, but it
//can be called include or anything else that is easy for you
//to remember or write, except "import", because it is reserved
//for future use.
var require = function(script_name) {
var uri = '';
if (script_name.indexOf('/') > -1) {
uri = script_name;
var lastSlash = uri.lastIndexOf('/');
script_name = uri.substring(lastSlash+1, uri.length);
}
else {
uri = _rmod.namespaceToUri(script_name, ivar._private.libpath);
}
if (!_rmod.loading.scripts.hasOwnProperty(script_name)
&& !_rmod.imported.hasOwnProperty(script_name)) {
_rmod.injectScript(script_name, uri,
_rmod.requireCallback,
_rmod.requirePrepare);
}
};
var ready = function(fn) {
_rmod.on_ready_fn_stack.push(fn);
};
This script will add a JavaScript file to the top of any other <script> tag:
(function () {
var li = document.createElement('script');
li.type = 'text/javascript';
li.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js";
li.async = true;
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(li, s);
})();
Keep it nice, short, simple, and maintainable! :]
// Third-party plugins / script (don't forget the full path is necessary)
var FULL_PATH = '', s =
[
FULL_PATH + 'plugins/script.js' // Script example
FULL_PATH + 'plugins/jquery.1.2.js', // jQuery Library
FULL_PATH + 'plugins/crypto-js/hmac-sha1.js', // CryptoJS
FULL_PATH + 'plugins/crypto-js/enc-base64-min.js' // CryptoJS
];
function load(url)
{
var ajax = new XMLHttpRequest();
ajax.open('GET', url, false);
ajax.onreadystatechange = function ()
{
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4)
{
switch(ajax.status)
{
case 200:
eval.apply( window, [script] );
console.log("library loaded: ", url);
break;
default:
console.log("ERROR: library not loaded: ", url);
}
}
};
ajax.send(null);
}
// Initialize a single load
load('plugins/script.js');
// Initialize a full load of scripts
if (s.length > 0)
{
for (i = 0; i < s.length; i++)
{
load(s[i]);
}
}
This code is simply a short functional example that could require additional feature functionality for full support on any (or given) platform.
I came to this question because I was looking for a simple way to maintain a collection of useful JavaScript plugins. After seeing some of the solutions here, I came up with this:
Set up a file called "plugins.js" (or extensions.js or whatever you want). Keep your plugin files together with that one master file.
plugins.js will have an array called pluginNames[] that we will iterate over each(),
then append a <script> tag to the head for each plugin
//set array to be updated when we add or remove plugin files
var pluginNames = ["lettering", "fittext", "butterjam", etc.];
//one script tag for each plugin
$.each(pluginNames, function(){
$('head').append('<script src="js/plugins/' + this + '.js"></script>');
});
Manually call just the one file in your head:
<script src="js/plugins/plugins.js"></script>
BUT:
Even though all of the plugins get dropped into the head tag the way they ought to, they don't always get run by the browser when you click into the page or refresh.
I've found it's more reliable to just write the script tags in a PHP include. You only have to write it once and that's just as much work as calling the plugin using JavaScript.
There are several ways to implement modules in JavaScript. Here are the two most popular ones:
ES6 Modules
Browsers do not support this moduling system yet, so in order for you to use this syntax you must use a bundler like Webpack. Using a bundler is better anyway because this can combine all of your different files into a single (or a couple of related) files. This will serve the files from the server to the client faster because each HTTP request has some associated overhead accompanied with it. Thus by reducing the overall HTTP request we improve the performance. Here is an example of ES6 modules:
// main.js file
export function add (a, b) {
return a + b;
}
export default function multiply (a, b) {
return a * b;
}
// test.js file
import {add}, multiply from './main'; // For named exports between curly braces {export1, export2}
// For default exports without {}
console.log(multiply(2, 2)); // logs 4
console.log(add(1, 2)); // logs 3
CommonJS (used in Node.js)
This moduling system is used in Node.js. You basically add your exports to an object which is called module.exports. You then can access this object via a require('modulePath'). Important here is to realize that these modules are being cached, so if you require() a certain module twice it will return the already created module.
// main.js file
function add (a, b) {
return a + b;
}
module.exports = add; // Here we add our 'add' function to the exports object
// test.js file
const add = require('./main');
console.log(add(1,2)); // logs 3
When loading scripts without using modules, I could use the document.currentscript to access custom attributes.
E.g.
<script src="js/myscript.js" data-custom-attribute="my-value"></script>
Within myscript.js I can then do the following
// will contain "my-value"
const myAttribute = document.currentScript.getAttribute('data-custom-attribute');
If I load the javascript using module syntax however, the currentScript is set to null and this doesn't work.
<script src="js/myscript.js" data-custom-attribute="my-value" type="module"></script>
Is there a way to still access such attributes within the javascript file?
From MDN
The Document.currentScript property returns the element whose
script is currently being processed and isn't a JavaScript module.
(For modules use import.meta instead.)
import.meta does not provide the data-attribute. Here are a few alternatives:
[edit may 2022] The import from the original snippet does not exist anymore. Though it's still loaded from cdn.jsdelivr.net, this may in the future not be the case. So, added a new snippet using a more persistent library.
<script data-custom-attribute="my-value" type="module">
import {Logger} from
"https://cdn.jsdelivr.net/gh/KooiInc/DOM-Utilities#v1.1.2/SmallHelpers.js";
const log = Logger();
log(`document.currentScript is ${document.currentScript}`);
log(`But with querySelector ... data-custom-attribute from module script: ${
document.querySelector("script[type=module]").dataset.customAttribute}`);
log(`Or more precize: document.querySelector("script[data-custom-attribute]"): ${
document.querySelector("script[data-custom-attribute]")
.dataset.customAttribute}`);
log(`Or retrieve and filter document.scripts: ${[...document.scripts]
.find(scrpt => scrpt.dataset.customAttribute).dataset.customAttribute}`);
</script>
<script type="module" data-custom-attribute="my-value">
import $ from "https://kooiinc.github.io/JQL/lib/JQLBundle.js";
$.setStyle(`#result`, {whiteSpace: `nowrap`});
$.setStyle(`#result div`, {marginTop: `0.3rem`});
$.setStyle(`code`, {color: `green`});
const log = (...lines) =>
lines.forEach( line => $(`#result`).html(`<div>${line}</div>`, true));
const indent = `<br> `;
// --------------------------------------------------------------------------
log(`<code>document.currentScript</code> = ${document.currentScript}`);
log(`But<br>
<code>document.querySelector("script[type=module]")
.dataset.customAttribute</code> = "${
document.querySelector("script[type=module]").dataset.customAttribute}"`);
log(`Or targeted exactly<br>
<code>document.querySelector("script[data-custom-attribute]")
${indent}.dataset.customAttribute</code> = "${
document.querySelector("script[data-custom-attribute]")
.dataset.customAttribute}"`);
log(`Or retrieve from <code>document.scripts</code><br>
<code>[...document.scripts].find(scrpt =>
${indent}scrpt.dataset.customAttribute).dataset.customAttribute</code> = "${
[...document.scripts].find(scrpt => scrpt.dataset.customAttribute)
.dataset.customAttribute}"`);
</script>
<div id="result"></result>
I don't have a solution to this problem, but I wanted to point out that there can also be a problem with non module scripts not showing document.currentScript.getAttribute(...). The problem may be specific to Firefox. Reference.
I've been experimenting with new native ECMAScript module support that has recently been added to browsers. It's pleasant to finally be able import scripts directly and cleanly from JavaScript.
/example.html 🔍
<script type="module">
import {example} from '/example.js';
example();
</script>
/example.js
export function example() {
document.body.appendChild(document.createTextNode("hello"));
};
However, this only allows me to import modules that are defined by separate external JavaScript files. I usually prefer to inline some scripts used for the initial rendering, so their requests don't block the rest of the page. With a traditional informally-structured library, that might look like this:
/inline-traditional.html 🔍
<body>
<script>
var example = {};
example.example = function() {
document.body.appendChild(document.createTextNode("hello"));
};
</script>
<script>
example.example();
</script>
However, naively inlining modules files obviously won't work, since it would remove the filename used to identify the module to other modules. HTTP/2 server push may be the canonical way to handle this situation, but it's still not an option in all environments.
Is it possible to perform an equivalent transformation with ECMAScript modules?
Is there any way for a <script type="module"> to import a module exported by another in the same document?
I imagine this could work by allowing the script to specify a file path, and behave as though it had already been downloaded or pushed from the path.
/inline-name.html 🔍
<script type="module" name="/example.js">
export function example() {
document.body.appendChild(document.createTextNode("hello"));
};
</script>
<script type="module">
import {example} from '/example.js';
example();
</script>
Or maybe by an entirely different reference scheme, such as is used for local SVG references:
/inline-id.html 🔍
<script type="module" id="example">
export function example() {
document.body.appendChild(document.createTextNode("hello"));
};
</script>
<script type="module">
import {example} from '#example';
example();
</script>
But neither of these hypotheticals actually work, and I haven't seen an alternative which does.
Hacking Together Our Own import from '#id'
Exports/imports between inline scripts aren't natively supported, but it was a fun exercise to hack together an implementation for my documents. Code-golfed down to a small block, I use it like this:
<script type="module" data-info="https://stackoverflow.com/a/43834063">let l,e,t
='script',p=/(from\s+|import\s+)['"](#[\w\-]+)['"]/g,x='textContent',d=document,
s,o;for(o of d.querySelectorAll(t+'[type=inline-module]'))l=d.createElement(t),o
.id?l.id=o.id:0,l.type='module',l[x]=o[x].replace(p,(u,a,z)=>(e=d.querySelector(
t+z+'[type=module][src]'))?a+`/* ${z} */'${e.src}'`:u),l.src=URL.createObjectURL
(new Blob([l[x]],{type:'application/java'+t})),o.replaceWith(l)//inline</script>
<script type="inline-module" id="utils">
let n = 1;
export const log = message => {
const output = document.createElement('pre');
output.textContent = `[${n++}] ${message}`;
document.body.appendChild(output);
};
</script>
<script type="inline-module" id="dogs">
import {log} from '#utils';
log("Exporting dog names.");
export const names = ["Kayla", "Bentley", "Gilligan"];
</script>
<script type="inline-module">
import {log} from '#utils';
import {names as dogNames} from '#dogs';
log(`Imported dog names: ${dogNames.join(", ")}.`);
</script>
Instead of <script type="module">, we need to define our script elements using a custom type like <script type="inline-module">. This prevents the browser from trying to execute their contents itself, leaving them for us to handle. The script (full version below) finds all inline-module script elements in the document, and transforms them into regular script module elements with the behaviour we want.
Inline scripts can't be directly imported from each other, so we need to give the scripts importable URLs. We generate a blob: URL for each of them, containing their code, and set the src attribute to run from that URL instead of running inline. The blob: URLs acts like normal URLs from the server, so they can be imported from other modules. Each time we see a subsequent inline-module trying to import from '#example', where example is the ID of a inline-module we've transformed, we modify that import to import from the blob: URL instead. This maintains the one-time execution and reference deduplication that modules are supposed to have.
<script type="module" id="dogs" src="blob:https://example.com/9dc17f20-04ab-44cd-906e">
import {log} from /* #utils */ 'blob:https://example.com/88fd6f1e-fdf4-4920-9a3b';
log("Exporting dog names.");
export const names = ["Kayla", "Bentley", "Gilligan"];
</script>
The execution of module script elements is always deferred until after the document is parsed, so we don't need to worry about trying to support the way that traditional script elements can modify the document while it's still being parsed.
export {};
for (const original of document.querySelectorAll('script[type=inline-module]')) {
const replacement = document.createElement('script');
// Preserve the ID so the element can be selected for import.
if (original.id) {
replacement.id = original.id;
}
replacement.type = 'module';
const transformedSource = original.textContent.replace(
// Find anything that looks like an import from '#some-id'.
/(from\s+|import\s+)['"](#[\w\-]+)['"]/g,
(unmodified, action, selector) => {
// If we can find a suitable script with that id...
const refEl = document.querySelector('script[type=module][src]' + selector);
return refEl ?
// ..then update the import to use that script's src URL instead.
`${action}/* ${selector} */ '${refEl.src}'` :
unmodified;
});
// Include the updated code in the src attribute as a blob URL that can be re-imported.
replacement.src = URL.createObjectURL(
new Blob([transformedSource], {type: 'application/javascript'}));
// Insert the updated code inline, for debugging (it will be ignored).
replacement.textContent = transformedSource;
original.replaceWith(replacement);
}
Warnings: this simple implementation doesn't handle script elements added after the initial document has been parsed, or allow script elements to import from other script elements that occur after them in the document. If you have both module and inline-module script elements in a document, their relative execution order may not be correct. The source code transformation is performed using a crude regex that won't handle some edge cases such as periods in IDs.
This is possible with service workers.
Since a service worker should be installed before it will be able to process a page, this requires to have a separate page to initialize a worker to avoid chicken/egg problem - or a page can reloaded when a worker is ready.
Example
Here's a demo that is supposed to be workable in modern browsers that support native ES modules and async..await (namely Chrome):
index.html
<html>
<head>
<script>
(async () => {
try {
const swInstalled = await navigator.serviceWorker.getRegistration('./');
await navigator.serviceWorker.register('sw.js', { scope: './' })
if (!swInstalled) {
location.reload();
}
} catch (err) {
console.error('Worker not registered', err);
}
})();
</script>
</head>
<body>
World,
<script type="module" data-name="./example.js">
export function example() {
document.body.appendChild(document.createTextNode("hello"));
};
</script>
<script type="module">
import {example} from './example.js';
example();
</script>
</body>
</html>
sw.js
self.addEventListener('fetch', e => {
// parsed pages
if (/^https:\/\/run.plnkr.co\/\w+\/$/.test(e.request.url)) {
e.respondWith(parseResponse(e.request));
// module files
} else if (cachedModules.has(e.request.url)) {
const moduleBody = cachedModules.get(e.request.url);
const response = new Response(moduleBody,
{ headers: new Headers({ 'Content-Type' : 'text/javascript' }) }
);
e.respondWith(response);
} else {
e.respondWith(fetch(e.request));
}
});
const cachedModules = new Map();
async function parseResponse(request) {
const response = await fetch(request);
if (!response.body)
return response;
const html = await response.text(); // HTML response can be modified further
const moduleRegex = /<script type="module" data-name="([\w./]+)">([\s\S]*?)<\/script>/;
const moduleScripts = html.match(new RegExp(moduleRegex.source, 'g'))
.map(moduleScript => moduleScript.match(moduleRegex));
for (const [, moduleName, moduleBody] of moduleScripts) {
const moduleUrl = new URL(moduleName, request.url).href;
cachedModules.set(moduleUrl, moduleBody);
}
const parsedResponse = new Response(html, response);
return parsedResponse;
}
Script bodies are being cached (native Cache can be used as well) and returned for respective module requests.
Concerns
The approach is inferior to the application built and chunked with bundling tool like Webpack or Rollup in terms of performance, flexibility, solidity and browser support - especially if blocking concurrent requests are the primary concern.
Inline scripts increase bandwidth usage. This is naturally avoided when scripts are loaded once and cached by the browser.
Inline scripts aren't modular and contradict the concept of ECMAScript modules (unless they are generated from real modules by server-side template).
Service worker initialization should be performed on a separate page to avoid unnecessary requests.
The solution is limited to a single page and doesn't take <base> into account.
A regular expression is used for demonstration purposes only. When used like in the example above it enables the execution of arbitrary JavaScript code that is available on the page. A proven library like parse5 should be used instead (it will result in performance overhead, and still, there may be security concerns). Never use regular expressions to parse the DOM.
I don't believe that's possible.
For inline scripts you're stuck with one of the more traditional ways of modularizing code, like the namespacing you demonstrated using object literals.
With webpack you can do code splitting which you could use to grab a very minimal chunk of code on page load and then incrementally grab the rest as needed. Webpack also has the advantage of allowing you to use the module syntax (plus a ton of other ES201X improvements) in way more environments than just Chrome Canary.
I tweaked Jeremy's answer with the use of this article to prevent scripts from executing
<script data-info="https://stackoverflow.com/a/43834063">
// awsome guy on [data-info] wrote 90% of this but I added the mutation/module-type part
let l,e,t='script',p=/(from\s+|import\s+)['"](#[\w\-]+)['"]/g,x='textContent',d=document,s,o;
let evls = event => (
event.target.type === 'javascript/blocked',
event.preventDefault(),
event.target.removeEventListener( 'beforescriptexecute', evls ) )
;(new MutationObserver( mutations =>
mutations.forEach( ({ addedNodes }) =>
addedNodes.forEach( node =>
( node.nodeType === 1 && node.matches( t+'[module-type=inline]' )
&& (
node.type = 'javascript/blocked',
node.addEventListener( 'beforescriptexecute', evls ),
o = node,
l=d.createElement(t),
o.id?l.id=o.id:0,
l.type='module',
l[x]=o[x].replace(p,(u,a,z)=>
(e=d.querySelector(t+z+'[type=module][src]'))
?a+`/* ${z} */'${e.src}'`
:u),
l.src=URL.createObjectURL(
new Blob([l[x]],
{type:'application/java'+t})),
o.replaceWith(l)
)//inline
) ) )))
.observe( document.documentElement, {
childList: true,
subtree: true
} )
// for(o of d.querySelectorAll(t+'[module-type=inline]'))
// l=d.createElement(t),
// o.id?l.id=o.id:0,
// l.type='module',
// l[x]=o[x].replace(p,(u,a,z)=>
// (e=d.querySelector(t+z+'[type=module][src]'))
// ?a+`/* ${z} */'${e.src}'`
// :u),
// l.src=URL.createObjectURL(
// new Blob([l[x]],
// {type:'application/java'+t})),
// o.replaceWith(l)//inline</script>
I'm hoping that this solves the dynamic-script-appending issue (using MutationObserver), vs-code not syntax-highlighting (preserving type=module) and I imagine that using the same MutationObserver one could execute scripts once the imported ids are added to the DOM.
Please tell me if this has issues!
We can use blob and importmap to import inline scripts.
https://github.com/xitu/inline-module
<div id="app"></div>
<script type="inline-module" id="foo">
const foo = 'bar';
export {foo};
</script>
<script src="https://unpkg.com/inline-module/index.js" setup></script>
<script type="module">
import {foo} from '#foo';
app.textContent = foo;
</script>
How do I include a JavaScript file inside another JavaScript file, similar to #import in CSS?
The old versions of JavaScript had no import, include, or require, so many different approaches to this problem have been developed.
But since 2015 (ES6), JavaScript has had the ES6 modules standard to import modules in Node.js, which is also supported by most modern browsers.
For compatibility with older browsers, build tools like Webpack and Rollup and/or transpilation tools like Babel can be used.
ES6 Modules
ECMAScript (ES6) modules have been supported in Node.js since v8.5, with the --experimental-modules flag, and since at least Node.js v13.8.0 without the flag. To enable "ESM" (vs. Node.js's previous CommonJS-style module system ["CJS"]) you either use "type": "module" in package.json or give the files the extension .mjs. (Similarly, modules written with Node.js's previous CJS module can be named .cjs if your default is ESM.)
Using package.json:
{
"type": "module"
}
Then module.js:
export function hello() {
return "Hello";
}
Then main.js:
import { hello } from './module.js';
let val = hello(); // val is "Hello";
Using .mjs, you'd have module.mjs:
export function hello() {
return "Hello";
}
Then main.mjs:
import { hello } from './module.mjs';
let val = hello(); // val is "Hello";
ECMAScript modules in browsers
Browsers have had support for loading ECMAScript modules directly (no tools like Webpack required) since Safari 10.1, Chrome 61, Firefox 60, and Edge 16. Check the current support at caniuse. There is no need to use Node.js' .mjs extension; browsers completely ignore file extensions on modules/scripts.
<script type="module">
import { hello } from './hello.mjs'; // Or the extension could be just `.js`
hello('world');
</script>
// hello.mjs -- or the extension could be just `.js`
export function hello(text) {
const div = document.createElement('div');
div.textContent = `Hello ${text}`;
document.body.appendChild(div);
}
Read more at https://jakearchibald.com/2017/es-modules-in-browsers/
Dynamic imports in browsers
Dynamic imports let the script load other scripts as needed:
<script type="module">
import('hello.mjs').then(module => {
module.hello('world');
});
</script>
Read more at https://developers.google.com/web/updates/2017/11/dynamic-import
Node.js require
The older CJS module style, still widely used in Node.js, is the module.exports/require system.
// mymodule.js
module.exports = {
hello: function() {
return "Hello";
}
}
// server.js
const myModule = require('./mymodule');
let val = myModule.hello(); // val is "Hello"
There are other ways for JavaScript to include external JavaScript contents in browsers that do not require preprocessing.
AJAX Loading
You could load an additional script with an AJAX call and then use eval to run it. This is the most straightforward way, but it is limited to your domain because of the JavaScript sandbox security model. Using eval also opens the door to bugs, hacks and security issues.
Fetch Loading
Like Dynamic Imports you can load one or many scripts with a fetch call using promises to control order of execution for script dependencies using the Fetch Inject library:
fetchInject([
'https://cdn.jsdelivr.net/momentjs/2.17.1/moment.min.js'
]).then(() => {
console.log(`Finish in less than ${moment().endOf('year').fromNow(true)}`)
})
jQuery Loading
The jQuery library provides loading functionality in one line:
$.getScript("my_lovely_script.js", function() {
alert("Script loaded but not necessarily executed.");
});
Dynamic Script Loading
You could add a script tag with the script URL into the HTML. To avoid the overhead of jQuery, this is an ideal solution.
The script can even reside on a different server. Furthermore, the browser evaluates the code. The <script> tag can be injected into either the web page <head>, or inserted just before the closing </body> tag.
Here is an example of how this could work:
function dynamicallyLoadScript(url) {
var script = document.createElement("script"); // create a script DOM node
script.src = url; // set its src to the provided URL
document.head.appendChild(script); // add it to the end of the head section of the page (could change 'head' to 'body' to add it to the end of the body section instead)
}
This function will add a new <script> tag to the end of the head section of the page, where the src attribute is set to the URL which is given to the function as the first parameter.
Both of these solutions are discussed and illustrated in JavaScript Madness: Dynamic Script Loading.
Detecting when the script has been executed
Now, there is a big issue you must know about. Doing that implies that you remotely load the code. Modern web browsers will load the file and keep executing your current script because they load everything asynchronously to improve performance. (This applies to both the jQuery method and the manual dynamic script loading method.)
It means that if you use these tricks directly, you won't be able to use your newly loaded code the next line after you asked it to be loaded, because it will be still loading.
For example: my_lovely_script.js contains MySuperObject:
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
var s = new MySuperObject();
Error : MySuperObject is undefined
Then you reload the page hitting F5. And it works! Confusing...
So what to do about it ?
Well, you can use the hack the author suggests in the link I gave you. In summary, for people in a hurry, he uses an event to run a callback function when the script is loaded. So you can put all the code using the remote library in the callback function. For example:
function loadScript(url, callback)
{
// Adding the script tag to the head as suggested before
var head = document.head;
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = url;
// Then bind the event to the callback function.
// There are several events for cross browser compatibility.
script.onreadystatechange = callback;
script.onload = callback;
// Fire the loading
head.appendChild(script);
}
Then you write the code you want to use AFTER the script is loaded in a lambda function:
var myPrettyCode = function() {
// Here, do whatever you want
};
Then you run all that:
loadScript("my_lovely_script.js", myPrettyCode);
Note that the script may execute after the DOM has loaded, or before, depending on the browser and whether you included the line script.async = false;. There's a great article on Javascript loading in general which discusses this.
Source Code Merge/Preprocessing
As mentioned at the top of this answer, many developers use build/transpilation tool(s) like Parcel, Webpack, or Babel in their projects, allowing them to use upcoming JavaScript syntax, provide backward compatibility for older browsers, combine files, minify, perform code splitting etc.
If anyone is looking for something more advanced, try out RequireJS. You'll get added benefits such as dependency management, better concurrency, and avoid duplication (that is, retrieving a script more than once).
You can write your JavaScript files in "modules" and then reference them as dependencies in other scripts. Or you can use RequireJS as a simple "go get this script" solution.
Example:
Define dependencies as modules:
some-dependency.js
define(['lib/dependency1', 'lib/dependency2'], function (d1, d2) {
//Your actual script goes here.
//The dependent scripts will be fetched if necessary.
return libraryObject; //For example, jQuery object
});
implementation.js is your "main" JavaScript file that depends on some-dependency.js
require(['some-dependency'], function(dependency) {
//Your script goes here
//some-dependency.js is fetched.
//Then your script is executed
});
Excerpt from the GitHub README:
RequireJS loads plain JavaScript files as well as more defined
modules. It is optimized for in-browser use, including in a Web
Worker, but it can be used in other JavaScript environments, like
Rhino and Node. It implements the Asynchronous Module API.
RequireJS uses plain script tags to load modules/files, so it should
allow for easy debugging. It can be used simply to load existing
JavaScript files, so you can add it to your existing project without
having to re-write your JavaScript files.
...
There actually is a way to load a JavaScript file not asynchronously, so you could use the functions included in your newly loaded file right after loading it, and I think it works in all browsers.
You need to use jQuery.append() on the <head> element of your page, that is:
$("head").append($("<script></script>").attr("src", url));
/* Note that following line of code is incorrect because it doesn't escape the
* HTML attribute src correctly and will fail if `url` contains special characters:
* $("head").append('<script src="' + url + '"></script>');
*/
However, this method also has a problem: if an error happens in the imported JavaScript file, Firebug (and also Firefox Error Console and Chrome Developer Tools as well) will report its place incorrectly, which is a big problem if you use Firebug to track JavaScript errors down a lot (I do). Firebug simply doesn't know about the newly loaded file for some reason, so if an error occurs in that file, it reports that it occurred in your main HTML file, and you will have trouble finding out the real reason for the error.
But if that is not a problem for you, then this method should work.
I have actually written a jQuery plugin called $.import_js() which uses this method:
(function($)
{
/*
* $.import_js() helper (for JavaScript importing within JavaScript code).
*/
var import_js_imported = [];
$.extend(true,
{
import_js : function(script)
{
var found = false;
for (var i = 0; i < import_js_imported.length; i++)
if (import_js_imported[i] == script) {
found = true;
break;
}
if (found == false) {
$("head").append($('<script></script').attr('src', script));
import_js_imported.push(script);
}
}
});
})(jQuery);
So all you would need to do to import JavaScript is:
$.import_js('/path_to_project/scripts/somefunctions.js');
I also made a simple test for this at Example.
It includes a main.js file in the main HTML and then the script in main.js uses $.import_js() to import an additional file called included.js, which defines this function:
function hello()
{
alert("Hello world!");
}
And right after including included.js, the hello() function is called, and you get the alert.
(This answer is in response to e-satis' comment).
Another way, that in my opinion is much cleaner, is to make a synchronous Ajax request instead of using a <script> tag. Which is also how Node.js handles includes.
Here's an example using jQuery:
function require(script) {
$.ajax({
url: script,
dataType: "script",
async: false, // <-- This is the key
success: function () {
// all good...
},
error: function () {
throw new Error("Could not load script " + script);
}
});
}
You can then use it in your code as you'd usually use an include:
require("/scripts/subscript.js");
And be able to call a function from the required script in the next line:
subscript.doSomethingCool();
It is possible to dynamically generate a JavaScript tag and append it to HTML document from inside other JavaScript code. This will load targeted JavaScript file.
function includeJs(jsFilePath) {
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
}
includeJs("/path/to/some/file.js");
There is a good news for you. Very soon you will be able to load JavaScript code easily. It will become a standard way of importing modules of JavaScript code and will be part of core JavaScript itself.
You simply have to write import cond from 'cond.js'; to load a macro named cond from a file cond.js.
So you don't have to rely upon any JavaScript framework nor do you have to explicitly make Ajax calls.
Refer to:
Static module resolution
Module loaders
Statement import is in ECMAScript 6.
Syntax
import name from "module-name";
import { member } from "module-name";
import { member as alias } from "module-name";
import { member1 , member2 } from "module-name";
import { member1 , member2 as alias2 , [...] } from "module-name";
import name , { member [ , [...] ] } from "module-name";
import "module-name" as name;
Maybe you can use this function that I found on this page How do I include a JavaScript file in a JavaScript file?:
function include(filename)
{
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.src = filename;
script.type = 'text/javascript';
head.appendChild(script)
}
Here is a synchronous version without jQuery:
function myRequire( url ) {
var ajax = new XMLHttpRequest();
ajax.open( 'GET', url, false ); // <-- the 'false' makes it synchronous
ajax.onreadystatechange = function () {
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4) {
switch( ajax.status) {
case 200:
eval.apply( window, [script] );
console.log("script loaded: ", url);
break;
default:
console.log("ERROR: script not loaded: ", url);
}
}
};
ajax.send(null);
}
Note that to get this working cross-domain, the server will need to set allow-origin header in its response.
I just wrote this JavaScript code (using Prototype for DOM manipulation):
var require = (function() {
var _required = {};
return (function(url, callback) {
if (typeof url == 'object') {
// We've (hopefully) got an array: time to chain!
if (url.length > 1) {
// Load the nth file as soon as everything up to the
// n-1th one is done.
require(url.slice(0, url.length - 1), function() {
require(url[url.length - 1], callback);
});
} else if (url.length == 1) {
require(url[0], callback);
}
return;
}
if (typeof _required[url] == 'undefined') {
// Haven't loaded this URL yet; gogogo!
_required[url] = [];
var script = new Element('script', {
src: url,
type: 'text/javascript'
});
script.observe('load', function() {
console.log("script " + url + " loaded.");
_required[url].each(function(cb) {
cb.call(); // TODO: does this execute in the right context?
});
_required[url] = true;
});
$$('head')[0].insert(script);
} else if (typeof _required[url] == 'boolean') {
// We already loaded the thing, so go ahead.
if (callback) {
callback.call();
}
return;
}
if (callback) {
_required[url].push(callback);
}
});
})();
Usage:
<script src="prototype.js"></script>
<script src="require.js"></script>
<script>
require(['foo.js','bar.js'], function () {
/* Use foo.js and bar.js here */
});
</script>
Gist: http://gist.github.com/284442.
If you want it in pure JavaScript, you can use document.write.
document.write('<script src="myscript.js" type="text/javascript"></script>');
If you use the jQuery library, you can use the $.getScript method.
$.getScript("another_script.js");
Here's the generalized version of how Facebook does it for their ubiquitous Like button:
<script>
var firstScript = document.getElementsByTagName('script')[0],
js = document.createElement('script');
js.src = 'https://cdnjs.cloudflare.com/ajax/libs/Snowstorm/20131208/snowstorm-min.js';
js.onload = function () {
// do stuff with your dynamically loaded script
snowStorm.snowColor = '#99ccff';
};
firstScript.parentNode.insertBefore(js, firstScript);
</script>
If it works for Facebook, it will work for you.
The reason why we look for the first script element instead of head or body is because some browsers don't create one if missing, but we're guaranteed to have a script element - this one. Read more at http://www.jspatterns.com/the-ridiculous-case-of-adding-a-script-element/.
You can also assemble your scripts using PHP:
File main.js.php:
<?php
header('Content-type:text/javascript; charset=utf-8');
include_once("foo.js.php");
include_once("bar.js.php");
?>
// Main JavaScript code goes here
Most of solutions shown here imply dynamical loading. I was searching instead for a compiler which assemble all the depended files into a single output file. The same as Less/Sass preprocessors deal with the CSS #import at-rule. Since I didn't find anything decent of this sort, I wrote a simple tool solving the issue.
So here is the compiler, https://github.com/dsheiko/jsic, which replaces $import("file-path") with the requested file content securely. Here is the corresponding Grunt plugin: https://github.com/dsheiko/grunt-jsic.
On the jQuery master branch, they simply concatenate atomic source files into a single one starting with intro.js and ending with outtro.js. That doesn't suits me as it provides no flexibility on the source code design. Check out how it works with jsic:
src/main.js
var foo = $import("./Form/Input/Tel");
src/Form/Input/Tel.js
function() {
return {
prop: "",
method: function(){}
}
}
Now we can run the compiler:
node jsic.js src/main.js build/mail.js
And get the combined file
build/main.js
var foo = function() {
return {
prop: "",
method: function(){}
}
};
If your intention to load the JavaScript file is using the functions from the imported/included file, you can also define a global object and set the functions as object items. For instance:
global.js
A = {};
file1.js
A.func1 = function() {
console.log("func1");
}
file2.js
A.func2 = function() {
console.log("func2");
}
main.js
A.func1();
A.func2();
You just need to be careful when you are including scripts in an HTML file. The order should be as in below:
<head>
<script type="text/javascript" src="global.js"></script>
<script type="text/javascript" src="file1.js"></script>
<script type="text/javascript" src="file2.js"></script>
<script type="text/javascript" src="main.js"></script>
</head>
This should do:
xhr = new XMLHttpRequest();
xhr.open("GET", "/soap/ajax/11.0/connection.js", false);
xhr.send();
eval(xhr.responseText);
Or rather than including at run time, use a script to concatenate prior to upload.
I use Sprockets (I don't know if there are others). You build your JavaScript code in separate files and include comments that are processed by the Sprockets engine as includes. For development you can include files sequentially, then for production to merge them...
See also:
Introducing Sprockets: JavaScript dependency management and concatenation
I had a simple issue, but I was baffled by responses to this question.
I had to use a variable (myVar1) defined in one JavaScript file (myvariables.js) in another JavaScript file (main.js).
For this I did as below:
Loaded the JavaScript code in the HTML file, in the correct order, myvariables.js first, then main.js:
<html>
<body onload="bodyReady();" >
<script src="myvariables.js" > </script>
<script src="main.js" > </script>
<!-- Some other code -->
</body>
</html>
File: myvariables.js
var myVar1 = "I am variable from myvariables.js";
File: main.js
// ...
function bodyReady() {
// ...
alert (myVar1); // This shows "I am variable from myvariables.js", which I needed
// ...
}
// ...
As you saw, I had use a variable in one JavaScript file in another JavaScript file, but I didn't need to include one in another. I just needed to ensure that the first JavaScript file loaded before the second JavaScript file, and, the first JavaScript file's variables are accessible in the second JavaScript file, automatically.
This saved my day. I hope this helps.
In a modern language with the check if script has already been loaded, it would be:
function loadJs( url ){
return new Promise(( resolve, reject ) => {
if (document.querySelector( `head > script[ src = "${url}" ]`) !== null ){
console.warn( `script already loaded: ${url}` );
resolve();
}
const script = document.createElement( "script" );
script.src = url;
script.onload = resolve;
script.onerror = function( reason ){
// This can be useful for your error-handling code
reason.message = `error trying to load script ${url}`;
reject( reason );
};
document.head.appendChild( script );
});
}
Usage (async/await):
try { await loadJs("https://.../script.js"); }
catch(error) { console.log(error); }
or
await loadJs( "https://.../script.js" ).catch( err => {} );
Usage (Promise):
loadJs( "https://.../script.js" ).then( res => {} ).catch( err => {} );
The #import syntax for achieving CSS-like JavaScript importing is possible using a tool such as Mixture via their special .mix file type (see here). I assume the application does this via one of above-mentioned methods.
From the Mixture documentation on .mix files:
Mix files are simply .js or .css files with .mix. in the file name. A
mix file simply extends the functionality of a normal style or
script file and allows you to import and combine.
Here's an example .mix file that combines multiple .js files into one:
// scripts-global.mix.js
// Plugins - Global
#import "global-plugins/headroom.js";
#import "global-plugins/retina-1.1.0.js";
#import "global-plugins/isotope.js";
#import "global-plugins/jquery.fitvids.js";
Mixture outputs this as scripts-global.js and also as a minified version (scripts-global.min.js).
Note: I'm not in any way affiliated with Mixture, other than using it as a front-end development tool. I came across this question upon seeing a .mix JavaScript file in action (in one of the Mixture boilerplates) and being a bit confused by it ("you can do this?" I thought to myself). Then I realized that it was an application-specific file type (somewhat disappointing, agreed). Nevertheless, figured the knowledge might be helpful for others.
Note: Mixture was discontinued on 2016/07/26 (after being open sourced on 2015/04/12).
ES6 Modules
Yes, use type="module" in a script tag (support):
<script type="module" src="script.js"></script>
And in a script.js file include another file like this:
import { hello } from './module.js';
...
// alert(hello());
In 'module.js' you must export the function/class that you will import:
export function hello() {
return "Hello World";
}
A working example is here.
In case you are using Web Workers and want to include additional scripts in the scope of the worker, the other answers provided about adding scripts to the head tag, etc. will not work for you.
Fortunately, Web Workers have their own importScripts function which is a global function in the scope of the Web Worker, native to the browser itself as it is part of the specification.
Alternatively, as the second highest voted answer to your question highlights, RequireJS can also handle including scripts inside a Web Worker (likely calling importScripts itself, but with a few other useful features).
Although these answers are great, there is a simple "solution" that has been around since script loading existed, and it will cover 99.999% of most people's use cases. Just include the script you need before the script that requires it. For most projects it does not take long to determine which scripts are needed and in what order.
<!DOCTYPE HTML>
<html>
<head>
<script src="script1.js"></script>
<script src="script2.js"></script>
</head>
<body></body>
</html>
If script2 requires script1, this really is the absolute easiest way to do something like this. I'm very surprised no-one has brought this up, as it's the most obvious and simplest answer that will apply in nearly every single case.
var js = document.createElement("script");
js.type = "text/javascript";
js.src = jsFilePath;
document.body.appendChild(js);
My usual method is:
var require = function (src, cb) {
cb = cb || function () {};
var newScriptTag = document.createElement('script'),
firstScriptTag = document.getElementsByTagName('script')[0];
newScriptTag.src = src;
newScriptTag.async = true;
newScriptTag.onload = newScriptTag.onreadystatechange = function () {
(!this.readyState || this.readyState === 'loaded' || this.readyState === 'complete') && (cb());
};
firstScriptTag.parentNode.insertBefore(newScriptTag, firstScriptTag);
}
It works great and uses no page-reloads for me. I've tried the AJAX method (one of the other answers) but it doesn't seem to work as nicely for me.
Here's an explanation of how the code works for those that are curious: essentially, it creates a new script tag (after the first one) of the URL. It sets it to asynchronous mode so it doesn't block the rest of the code, but calls a callback when the readyState (the state of the content to be loaded) changes to 'loaded'.
I wrote a simple module that automates the job of importing/including module scripts in JavaScript. For detailed explanation of the code, refer to the blog post JavaScript require / import / include modules.
// ----- USAGE -----
require('ivar.util.string');
require('ivar.net.*');
require('ivar/util/array.js');
require('http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js');
ready(function(){
//Do something when required scripts are loaded
});
//--------------------
var _rmod = _rmod || {}; //Require module namespace
_rmod.LOADED = false;
_rmod.on_ready_fn_stack = [];
_rmod.libpath = '';
_rmod.imported = {};
_rmod.loading = {
scripts: {},
length: 0
};
_rmod.findScriptPath = function(script_name) {
var script_elems = document.getElementsByTagName('script');
for (var i = 0; i < script_elems.length; i++) {
if (script_elems[i].src.endsWith(script_name)) {
var href = window.location.href;
href = href.substring(0, href.lastIndexOf('/'));
var url = script_elems[i].src.substring(0, script_elems[i].length - script_name.length);
return url.substring(href.length+1, url.length);
}
}
return '';
};
_rmod.libpath = _rmod.findScriptPath('script.js'); //Path of your main script used to mark
//the root directory of your library, any library.
_rmod.injectScript = function(script_name, uri, callback, prepare) {
if(!prepare)
prepare(script_name, uri);
var script_elem = document.createElement('script');
script_elem.type = 'text/javascript';
script_elem.title = script_name;
script_elem.src = uri;
script_elem.async = true;
script_elem.defer = false;
if(!callback)
script_elem.onload = function() {
callback(script_name, uri);
};
document.getElementsByTagName('head')[0].appendChild(script_elem);
};
_rmod.requirePrepare = function(script_name, uri) {
_rmod.loading.scripts[script_name] = uri;
_rmod.loading.length++;
};
_rmod.requireCallback = function(script_name, uri) {
_rmod.loading.length--;
delete _rmod.loading.scripts[script_name];
_rmod.imported[script_name] = uri;
if(_rmod.loading.length == 0)
_rmod.onReady();
};
_rmod.onReady = function() {
if (!_rmod.LOADED) {
for (var i = 0; i < _rmod.on_ready_fn_stack.length; i++){
_rmod.on_ready_fn_stack[i]();
});
_rmod.LOADED = true;
}
};
_.rmod = namespaceToUri = function(script_name, url) {
var np = script_name.split('.');
if (np.getLast() === '*') {
np.pop();
np.push('_all');
}
if(!url)
url = '';
script_name = np.join('.');
return url + np.join('/')+'.js';
};
//You can rename based on your liking. I chose require, but it
//can be called include or anything else that is easy for you
//to remember or write, except "import", because it is reserved
//for future use.
var require = function(script_name) {
var uri = '';
if (script_name.indexOf('/') > -1) {
uri = script_name;
var lastSlash = uri.lastIndexOf('/');
script_name = uri.substring(lastSlash+1, uri.length);
}
else {
uri = _rmod.namespaceToUri(script_name, ivar._private.libpath);
}
if (!_rmod.loading.scripts.hasOwnProperty(script_name)
&& !_rmod.imported.hasOwnProperty(script_name)) {
_rmod.injectScript(script_name, uri,
_rmod.requireCallback,
_rmod.requirePrepare);
}
};
var ready = function(fn) {
_rmod.on_ready_fn_stack.push(fn);
};
This script will add a JavaScript file to the top of any other <script> tag:
(function () {
var li = document.createElement('script');
li.type = 'text/javascript';
li.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js";
li.async = true;
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(li, s);
})();
Keep it nice, short, simple, and maintainable! :]
// Third-party plugins / script (don't forget the full path is necessary)
var FULL_PATH = '', s =
[
FULL_PATH + 'plugins/script.js' // Script example
FULL_PATH + 'plugins/jquery.1.2.js', // jQuery Library
FULL_PATH + 'plugins/crypto-js/hmac-sha1.js', // CryptoJS
FULL_PATH + 'plugins/crypto-js/enc-base64-min.js' // CryptoJS
];
function load(url)
{
var ajax = new XMLHttpRequest();
ajax.open('GET', url, false);
ajax.onreadystatechange = function ()
{
var script = ajax.response || ajax.responseText;
if (ajax.readyState === 4)
{
switch(ajax.status)
{
case 200:
eval.apply( window, [script] );
console.log("library loaded: ", url);
break;
default:
console.log("ERROR: library not loaded: ", url);
}
}
};
ajax.send(null);
}
// Initialize a single load
load('plugins/script.js');
// Initialize a full load of scripts
if (s.length > 0)
{
for (i = 0; i < s.length; i++)
{
load(s[i]);
}
}
This code is simply a short functional example that could require additional feature functionality for full support on any (or given) platform.
I came to this question because I was looking for a simple way to maintain a collection of useful JavaScript plugins. After seeing some of the solutions here, I came up with this:
Set up a file called "plugins.js" (or extensions.js or whatever you want). Keep your plugin files together with that one master file.
plugins.js will have an array called pluginNames[] that we will iterate over each(),
then append a <script> tag to the head for each plugin
//set array to be updated when we add or remove plugin files
var pluginNames = ["lettering", "fittext", "butterjam", etc.];
//one script tag for each plugin
$.each(pluginNames, function(){
$('head').append('<script src="js/plugins/' + this + '.js"></script>');
});
Manually call just the one file in your head:
<script src="js/plugins/plugins.js"></script>
BUT:
Even though all of the plugins get dropped into the head tag the way they ought to, they don't always get run by the browser when you click into the page or refresh.
I've found it's more reliable to just write the script tags in a PHP include. You only have to write it once and that's just as much work as calling the plugin using JavaScript.
There are several ways to implement modules in JavaScript. Here are the two most popular ones:
ES6 Modules
Browsers do not support this moduling system yet, so in order for you to use this syntax you must use a bundler like Webpack. Using a bundler is better anyway because this can combine all of your different files into a single (or a couple of related) files. This will serve the files from the server to the client faster because each HTTP request has some associated overhead accompanied with it. Thus by reducing the overall HTTP request we improve the performance. Here is an example of ES6 modules:
// main.js file
export function add (a, b) {
return a + b;
}
export default function multiply (a, b) {
return a * b;
}
// test.js file
import {add}, multiply from './main'; // For named exports between curly braces {export1, export2}
// For default exports without {}
console.log(multiply(2, 2)); // logs 4
console.log(add(1, 2)); // logs 3
CommonJS (used in Node.js)
This moduling system is used in Node.js. You basically add your exports to an object which is called module.exports. You then can access this object via a require('modulePath'). Important here is to realize that these modules are being cached, so if you require() a certain module twice it will return the already created module.
// main.js file
function add (a, b) {
return a + b;
}
module.exports = add; // Here we add our 'add' function to the exports object
// test.js file
const add = require('./main');
console.log(add(1,2)); // logs 3