We Keep Coding

Catch script tags 404

Is it possible to catch <script type="text/javascript" src=".."> 404 with JavaScript so that I could correct src?
window.onerror doesn't seem to catch these.
Important note! This script is dynamically added into body by 3rd-party library, so I have no control over it.
It would be so nice if I could detect the script insertion or src setting and update it with correct src like I could do with image but I think it's not possible with script element?
var NativeImage = window.Image;
class MyImage {
constructor (w, h) {
var nativeImage = new NativeImage(w, h);
var handler = {
set: function (obj, prop, value) {
if (prop === 'src') {
return nativeImage[prop] = '/correct/image/path.jpg';
}
return nativeImage[prop] = value;
},
get: function (target, prop) {
return target[prop];
}
};
return new Proxy(nativeImage, handler);
}
}
window.Image = MyImage;

You can detect the script's insertion with MutationObserver and add an error listener to the tag:
// Your code (run this before the external script)
new MutationObserver((mutations, observer) => {
for (const mutation of mutations) {
for (const node of mutation.addedNodes) {
// Add additional checks here if needed
// to identify if the script is the one added by the library
if (node.nodeType === 1 && node.matches('script')) {
node.addEventListener('error', () => {
console.log('Script could not be loaded');
});
// Remove the observer, since its purpose is fulfilled
observer.disconnect();
return;
}
}
}
})
// Watch for elements that are added as children to document.body:
.observe(document.body, { childList: true });
<script>
// External script:
window.addEventListener('DOMContentLoaded', () => {
const script = document.createElement('script');
script.src = 'doesntexist';
document.body.appendChild(script);
});
</script>

You can check the HTTP Status of your script src by sending a XMLHttpRequest:
HTTP Status Code from URL in Javascript
function getStatus(url) {
var request = new XMLHttpRequest();
request.onreadystatechange = function() {
if (request.readyState === 4){
return request.status;
};
request.open("GET", url, true);
request.send();
}

Include multiple javascript files in a JS file

So, if I have to include a Javascript file in a .js file, I use to below script. It works fine.
var script = document.createElement("SCRIPT");
script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js';
script.type = 'text/javascript';
script.onload = function() {
//Some code
};
document.getElementsByTagName("head")[0].appendChild(script);
What should I do If I need to include more than 1 files.

You can make a function and pass the js files you want to include like so:
function scriptLoader(path, callback)
{
var script = document.createElement('script');
script.type = "text/javascript";
script.async = true;
script.src = path;
script.onload = function(){
if(typeof(callback) == "function")
{
callback();
}
}
try
{
var scriptOne = document.getElementsByTagName('script')[0];
scriptOne.parentNode.insertBefore(script, scriptOne);
}
catch(e)
{
document.getElementsByTagName("head")[0].appendChild(script);
}
}
And call it like so:
scriptLoader('/path/to/file.js');
in the similar manner you can call as many JS file you like this:
scriptLoader('/path/to/file2.js');
scriptLoader('/path/to/file3.js');
and even with onload callback functions like so:
scriptLoader('/path/to/file6.js',function(){
alert('file6 loaded');
});

I would imagine you'd do the same as you've got there but just change the variable name from var script to something like var scriptA and change the code that follows to match like script.src = to scriptA.src =

This function will load one script or many, pass a single file or an array of many:
function include(src, cb) {
arr = (src instanceof Array) ? src : [{
'src': src,
'cb': cb
}];
arr.forEach(function(item) {
_include(item.src, item.cb);
})
function _include(src, cb) {
var script = document.createElement("SCRIPT");
script.src = src;
script.async = true;
script.type = 'text/javascript';
script.onload = function() {
if (cb) cb()
}
document.getElementsByTagName("head")[0].appendChild(script);
}
}
include("/js/file1.js");
include("/js/file1.js", function(){console.log("file1 loaded")});
include([{src:"/js/file1.js"},{src:"/js/file2.js"},{src:"/js/file3.js"}]);

Function return from XMLHttpRequest [duplicate]

I'm trying to load JS scripts dynamically, but using jQuery is not an option.
I checked jQuery source to see how getScript was implemented so that I could use that approach to load scripts using native JS. However, getScript only calls jQuery.get()
and I haven't been able to find where the get method is implemented.
So my question is,
What's a reliable way to implement my own getScript method using native JavaScript?
Thanks!

Here's a jQuery getScript alternative with callback functionality:
function getScript(source, callback) {
var script = document.createElement('script');
var prior = document.getElementsByTagName('script')[0];
script.async = 1;
script.onload = script.onreadystatechange = function( _, isAbort ) {
if(isAbort || !script.readyState || /loaded|complete/.test(script.readyState) ) {
script.onload = script.onreadystatechange = null;
script = undefined;
if(!isAbort && callback) setTimeout(callback, 0);
}
};
script.src = source;
prior.parentNode.insertBefore(script, prior);
}

You can fetch scripts like this:
(function(document, tag) {
var scriptTag = document.createElement(tag), // create a script tag
firstScriptTag = document.getElementsByTagName(tag)[0]; // find the first script tag in the document
scriptTag.src = 'your-script.js'; // set the source of the script to your script
firstScriptTag.parentNode.insertBefore(scriptTag, firstScriptTag); // append the script to the DOM
}(document, 'script'));

use this
var js_script = document.createElement('script');
js_script.type = "text/javascript";
js_script.src = "http://www.example.com/script.js";
js_script.async = true;
document.getElementsByTagName('head')[0].appendChild(js_script);

Firstly, Thanks for #Mahn's answer. I rewrote his solution in ES6 and promise, in case someone need it, I will just paste my code here:
const loadScript = (source, beforeEl, async = true, defer = true) => {
return new Promise((resolve, reject) => {
let script = document.createElement('script');
const prior = beforeEl || document.getElementsByTagName('script')[0];
script.async = async;
script.defer = defer;
function onloadHander(_, isAbort) {
if (isAbort || !script.readyState || /loaded|complete/.test(script.readyState)) {
script.onload = null;
script.onreadystatechange = null;
script = undefined;
if (isAbort) { reject(); } else { resolve(); }
}
}
script.onload = onloadHander;
script.onreadystatechange = onloadHander;
script.src = source;
prior.parentNode.insertBefore(script, prior);
});
}
Usage:
const scriptUrl = 'https://www.google.com/recaptcha/api.js?onload=onRecaptchaLoad&render=explicit';
loadScript(scriptUrl).then(() => {
console.log('script loaded');
}, () => {
console.log('fail to load script');
});
and code is eslinted.

This polishes up previous ES6 solutions and will work in all modern browsers
Load and Get Script as a Promise
const getScript = url => new Promise((resolve, reject) => {
const script = document.createElement('script')
script.src = url
script.async = true
script.onerror = reject
script.onload = script.onreadystatechange = function() {
const loadState = this.readyState
if (loadState && loadState !== 'loaded' && loadState !== 'complete') return
script.onload = script.onreadystatechange = null
resolve()
}
document.head.appendChild(script)
})
Usage
getScript('https://dummyjs.com/js')
.then(() => {
console.log('Loaded', dummy.text())
})
.catch(() => {
console.error('Could not load script')
})
Also works for JSONP endpoints
const callbackName = `_${Date.now()}`
getScript('http://example.com/jsonp?callback=' + callbackName)
.then(() => {
const data = window[callbackName];
console.log('Loaded', data)
})
Also, please be careful with some of the AJAX solutions listed as they are bound to the CORS policy in modern browsers https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

There are some good solutions here but many are outdated. There is a good one by #Mahn but as stated in a comment it is not exactly a replacement for $.getScript() as the callback does not receive data. I had already written my own function for a replacement for $.get() and landed here when I need it to work for a script. I was able to use #Mahn's solution and modify it a bit along with my current $.get() replacement and come up with something that works well and is simple to implement.
function pullScript(url, callback){
pull(url, function loadReturn(data, status, xhr){
//If call returned with a good status
if(status == 200){
var script = document.createElement('script');
//Instead of setting .src set .innerHTML
script.innerHTML = data;
document.querySelector('head').appendChild(script);
}
if(typeof callback != 'undefined'){
//If callback was given skip an execution frame and run callback passing relevant arguments
setTimeout(function runCallback(){callback(data, status, xhr)}, 0);
}
});
}
function pull(url, callback, method = 'GET', async = true) {
//Make sure we have a good method to run
method = method.toUpperCase();
if(!(method === 'GET' || method === 'POST' || method === 'HEAD')){
throw new Error('method must either be GET, POST, or HEAD');
}
//Setup our request
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState == XMLHttpRequest.DONE) { // XMLHttpRequest.DONE == 4
//Once the request has completed fire the callback with relevant arguments
//you should handle in your callback if it was successful or not
callback(xhr.responseText, xhr.status, xhr);
}
};
//Open and send request
xhr.open(method, url, async);
xhr.send();
}
Now we have a replacement for $.get() and $.getScript() that work just as simply:
pullScript(file1, function(data, status, xhr){
console.log(data);
console.log(status);
console.log(xhr);
});
pullScript(file2);
pull(file3, function loadReturn(data, status){
if(status == 200){
document.querySelector('#content').innerHTML = data;
}
}

Mozilla Developer Network provides an example that works asynchronously and does not use 'onreadystatechange' (from #ShaneX's answer) that is not really present in a HTMLScriptTag:
function loadError(oError) {
throw new URIError("The script " + oError.target.src + " didn't load correctly.");
}
function prefixScript(url, onloadFunction) {
var newScript = document.createElement("script");
newScript.onerror = loadError;
if (onloadFunction) { newScript.onload = onloadFunction; }
document.currentScript.parentNode.insertBefore(newScript, document.currentScript);
newScript.src = url;
}
Sample usage:
prefixScript("myScript1.js");
prefixScript("myScript2.js", function () { alert("The script \"myScript2.js\" has been correctly loaded."); });
But #Agamemnus' comment should be considered: The script might not be fully loaded when onloadFunction is called. A timer could be used setTimeout(func, 0) to let the event loop finalize the added script to the document. The event loop finally calls the function behind the timer and the script should be ready to use at this point.
However, maybe one should consider returning a Promise instead of providing two functions for exception & success handling, that would be the ES6 way. This would also render the need for a timer unnecessary, because Promises are handled by the event loop - becuase by the time the Promise is handled, the script was already finalized by the event loop.
Implementing Mozilla's method including Promises, the final code looks like this:
function loadScript(url)
{
return new Promise(function(resolve, reject)
{
let newScript = document.createElement("script");
newScript.onerror = reject;
newScript.onload = resolve;
document.currentScript.parentNode.insertBefore(newScript, document.currentScript);
newScript.src = url;
});
}
loadScript("test.js").then(() => { FunctionFromExportedScript(); }).catch(() => { console.log("rejected!"); });

window.addEventListener('DOMContentLoaded',
function() {
var head = document.getElementsByTagName('HEAD')[0];
var script = document.createElement('script');
script.src = "/Content/index.js";
head.appendChild(script);
});

Here's a version that preserves the accept and x-requested-with headers, like jquery getScript:
function pullScript(url, callback){
pull(url, function loadReturn(data, status, xhr){
if(status === 200){
var script = document.createElement('script');
script.innerHTML = data; // Instead of setting .src set .innerHTML
document.querySelector('head').appendChild(script);
}
if (typeof callback != 'undefined'){
// If callback was given skip an execution frame and run callback passing relevant arguments
setTimeout(function runCallback(){callback(data, status, xhr)}, 0);
}
});
}
function pull(url, callback) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState === XMLHttpRequest.DONE) {
callback(xhr.responseText, xhr.status, xhr);
}
};
xhr.open('GET', url, true);
xhr.setRequestHeader('accept', '*/*;q=0.5, text/javascript, application/javascript, application/ecmascript, application/x-ecmascript');
xhr.setRequestHeader('x-requested-with', 'XMLHttpRequest');
xhr.send();
}
pullScript(URL);

Best way to asynchronously load external js files via Promises

I am building a website that uses some external js files. I load the files via the code below, but I am not sure how to proceed if one or more of the files fails downloading. Should I just keep requesting them until all of them download? Is it better to do a separate onload event for each file? How would I know which file has failed loading and needs to be requested again?
var filesToLoad = ["https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"];
var loader = new ScriptLoader();
filesToLoad.forEach(function(file) {
loader.add(file);
});
loader.loaded(function(failedCallbackF) {
console.log("Error.");
//Try getting the files again??
});
function ScriptLoader() {
var promises = [];
this.add = function(url) {
var promise = new Promise(function(resolve, reject) {
var script = document.createElement('script');
script.src = url;
script.addEventListener('load', function() {
resolve(script);
}, false);
script.addEventListener('error', function() {
reject(script);
console.log('was rej');
}, false);
document.body.appendChild(script);
});
promises.push(promise);
};
this.loaded = function(callbackOnFailed) {
Promise.all(promises).then(function(result1) {
console.log('Script loaded from:', result1);
}, callbackOnFailed);
};
}

Well, there is an official API for it called "dynamic import", I recommend that you use it or shim it (with something like SystemJS or with a tool that supports it like webpack).
import("yourScriptFile.js").then(function(){
// script loaded.
});
If you want to load multiple files you can also use it:
Promise.all(["url1", "url2"].map(System.import)).then(function(){
// loaded all here
});

May be this will help you.
var filesToLoad = ["https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"];
filesToLoad.forEach(function(file) {
var loader = new ScriptLoader();
loader.add(file)
loader.loaded(function(failedCallbackF) {
console.log("Error.");
//reload this file
});
});
function ScriptLoader() {
var promises = [];
this.add = function(url) {
var promise = new Promise(function(resolve, reject) {
var script = document.createElement('script');
script.src = url;
script.addEventListener('load', function() {
resolve(script);
}, false);
script.addEventListener('error', function() {
reject(script);
console.log('was rej');
}, false);
document.body.appendChild(script);
});
promises.push(promise);
};
this.loaded = function(callbackOnFailed) {
Promise.all(promises).then(function(result1) {
console.log('Script loaded from:', result1);
}, callbackOnFailed);
};
}

Load External JavaScript File

I am trying to load an external javascript file from within javascript but I cannot seem to get it to work. Am I doing something wrong?
sample file of my work
function loadJs() {
var fileref=document.createElement('script')
fileref.setAttribute("type","text/javascript")
fileref.setAttribute("src", "https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js")
document.body.appendChild(fileref); }

Perhaps you are trying to access the jQuery API before it is fully loaded. You can add a callback parameter to the loadJs function like this:
function loadJs(src, callback) {
var s = document.createElement('script');
document.getElementsByTagName('head')[0].appendChild(s);
s.onload = function() {
//callback if existent.
if (typeof callback == "function") callback();
callback = null;
}
s.onreadystatechange = function() {
if (s.readyState == 4 || s.readyState == "complete") {
if (typeof callback == "function") callback();
callback = null; // Wipe callback, to prevent multiple calls.
}
}
s.src = src;
}
loadJs('https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js', function() {
$('body').append('<p>It works!</p>');
});
Tested in chrome, FF, ie8. Fiddle: http://jsfiddle.net/Umwbx/2/

Use code similar to this:
function loadJs() {
var s = document.createElement('script');
var c = document.getElementsByTagName('script')[0];
s.type = 'text/javascript';
s.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js';
c.parentNode.insertBefore(s, c);
}