The package smooth-scroll does not support ES2015 import.
I want to offer a pull request with support for import.
According to the docs I need to add the following line:
export default smoothScrollFunction;
However the package start with a self-invoking method and I am not sure how to proceed? How do you export a self invoking method?
code:
(function (root, factory) {
if ( typeof define === 'function' && define.amd ) {
define([], factory(root));
} else if ( typeof exports === 'object' ) {
module.exports = factory(root);
} else {
root.smoothScroll = factory(root);
}
})(typeof global !== 'undefined' ? global : this.window || this.global, (function (root) {
'use strict';
//
// more code...
//
ES2015 import/export statements require transpilation as no environment currently supports them. When transpiled they will be transformed into something that is supported by the target environment. If your target is Node this means that export statements would become module.exports = ..., or if your target is the browser then your modules will likely be bundled and wrapped in such a way that they are require-able, e.g. as in Browserify and Webpack.
Does it mean it's ES2015 import ready?
Practically, yes. Modules do not need to use the import/export in order to be ES2015 import friendly because actually no environment is, we just transform the import/export syntax in a way that makes it compatible.
In particular, with the module you have shared, you can import smoothScrollFunction from 'smooth-scroll' without the module itself containing an export smoothScrollFunction statement, as your import statement will be transpiled to (something like) var smoothScrollFunction = require('smooth-scroll') anyway.
Having said all this, in order to address the question in its entirety, you would amend an IIFE1 to be strictly ES2015 import compatible by removing the IIFE altogether, as ES2015 modules are standalone and have their own scope, much like modules in Node. You would however be dropping support for browsers, which undermines the purpose of using the IIFE / UMD2 approach.
For example (remember that this is not actually necessary!), we would take whatever the return value of the factory function is, along with anything that occurs before it, and move this out of the factory function. We would then export default the return value of the factory function.
// Anything before the return statement
// in the factory function goes here
export default // Return value of factory function goes here
1IIFE: immediately invoked function expression
2UMD: universal module declaration
How do I require a JavaScript library that is not packaged as a UMD-compatible module (AMD, CommonJS) with webpack?
I don't want the library to pass through a loader. I just want it to be included in a <script> tag whenever it is required, and for webpack to manage this dependency.
I don't want to simply place it in a script tag in my index.html, because I want to take advantage of webpack's code-splitting, and only include it when necessary.
I've read about 'externals', I'm not sure if this has anything to do with it. The docs are not clear enough.
Thanks :)
Updated question
Also this question is specifically about front-end libraries that only need to be included via a <script> tag to work.
You can add amd support to your library and then load it with webpack.
Some links that can help you achieve are:
http://ifandelse.com/its-not-hard-making-your-library-support-amd-and-commonjs/
https://github.com/mbostock/d3/pull/1921
What is basically being done is that at the top of your library you can check whether it's a commonjs environment or an AMD environment. Accordingly you can export your library.
One example can be this ( taken from 1st link )
(function (root, factory) {
if(typeof define === "function" && define.amd) {
// Now we're wrapping the factory and assigning the return
// value to the root (window) and returning it as well to
// the AMD loader.
define(["postal"], function(postal){
return (root.myModule = factory(postal));
});
} else if(typeof module === "object" && module.exports) {
// I've not encountered a need for this yet, since I haven't
// run into a scenario where plain modules depend on CommonJS
// *and* I happen to be loading in a CJS browser environment
// but I'm including it for the sake of being thorough
module.exports = (root.myModule = factory(require("postal")));
} else {
root.myModule = factory(root.postal);
}
}(this, function(postal) {
// module code here....
return myModule;
}));
OK, I am using ES6 and ReactJS, some packages you should do import React from "react"; in order to have them working, but others <script src="/semantic/dist/semantic.min.js"></script> in index.html, so, what cases should I apply one or another ?
In general, there are two types of modules. ES6 and non-ES6. If you want to use a non-ES6 modules with ES6, you can try one of the following approaches:
Compile with the CommonJS (for example using jQuery as CommonJS through npm)
Load with SystemJS to allow ES6 to work with CommonJS, AMD and globals
If you don't want to do this, you can try importing the non-ES6 scripts in HTML. In which case, you won't be doing something like
import $ from 'jquery';
So in short, if you want to use a non-ES6 module without compiling with CommonJS or if it is not available through npm, you can use HTML imports instead of ES6 import
I came across this question in the following situation: I want to use the react and react-dom api in a script I'm writing for a local index.html file. I can put a <script src="react-cdn-url"></script> tag in the <head> of index.html, but I would prefer to have the apis on my local system. So I wget react-cdn-url and see if I can just import it. I get some error on the console, so I look at the react.js file I now have and see the following lines:
(function (global, factory) {
typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
typeof define === 'function' && define.amd ? define(factory) :
(global.React = factory());
}(this, (function () { 'use strict';
...
})));
Once I decipher this, I should be able to make my react api "importable." So let's peel this apart bit by bit. First construct:
(function (global,factory){}(this,(function() {...})));
This is a bit confusing at first, so first look at the expression: (function (params){}(args)); The purpose of this is to create an unnamed function which takes paramaters params, then immediately call it with arguments arg. Contrast this with ;function (params){}(args);. This is not valid javascript, if you try it in node you sort of break the parser, if you do it in firefox console you'll get the error: SyntaxError: function statement requires a name. The reason why is that this is an incomplete syntactic construct. Javascript grammar allows you to write a function definition without a bound name, but this only makes sense in an expression. Enclosing the function definition in parenthesis causes it to be evaluated. Putting this all together we have an unnamed function being called on arguments this and (function(){}) (another unnamed function). this will be whatever the local context is, and the unnamed function corresponds to the factory parameter in the "top-level" anonymous function. Consider the following three lines:
typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
typeof define === 'function' && define.amd ? define(factory) :
(global.React = factory());
These check to see if this module is being imported from node, if so, it exports the result of the factory function. If it is being imported by require.js, it "defines" the factory function, if neither of these then the result of factory is given the name 'React' in the global object. This last case applies when "importing" the library through a <script> tag.
However, none of these cases really apply if you try to es6 import it. In order to make the import work as desired we will just export the factory function, then call it in the importing script. Why not just call the factory function and assign it to a name for export? Because you will need to pass the result of this factory to the factory for react-dom. In general, there are many issues continuing down this path, and eventually it will be better to settle upon some sort of dependency manager, but for now we keep playing.
let ReactFactory;
export default ReactFactory = function () { 'use strict';
...
}
I do the same thing to the react-dom file, changing these lines:
(function (global, factory) {
typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory(require('react')) :
typeof define === 'function' && define.amd ? define(['react'], factory) :
(global.ReactDOM = factory(global.React));
}(this, (function (React) { 'use strict';
...
})));
into:
let ReactDOMFactory;
export default ReactDOMFactory = function (React) { 'use strict';
...
}
Note that this time the factory function has the parameter React. I see a few lines down:
if (!React) {
{
throw Error("ReactDOM was loaded before React. Make sure you load the React package before loading ReactDOM.");
}
}
From this I take the hint that I need to create my React object from my first factory and pass it into the ReactDOMFactory. All in all, I put the following lines in my script.js file:
import ReactFactory from '/path-to-modified/react.js';
import ReactDOMFactory from '/path-to-modified/react-dom.js';
let React = ReactFactory();
let ReactDOM = ReactDOMFactory(React);
Where, of course, path-to-modified is the path to the modified api files, and voila! Now it works just fine.
I'm trying to include IOUtil.js and ChannelReplacement.js in my add-on, using the Cu.import(...) function. These two both use xpcom_generateQI, which I'm trying to obtain from the XPCOM jsm, but the two scripts cant access it.
const {Cc, Ci, Cu, Cr} = require("chrome");
Cu.import("resource://gre/modules/XPCOMUtils.jsm");
const xpcom_generateQI = XPCOMUtils.generateQI;
Cu.import(self.data.url("IOUtil.js"));
Cu.import(self.data.url("ChannelReplacement.js"));
gives me xpcom_generateQI is not defined.
How do I access a function which is defined in main.js?
Issues
Don't use Cu.import for local SDK modules. Don't write JS code modules for SDK add-ons, the SDK uses CommonJS-style modules together with the require() facility which also comes with proper cleanup for free, which cannot be said for JS code modules and Cu.import (you'd need to properly Cu.unload everything and likely kill some references yourself).
That https-everywhere stuff are neither JS code modules nor SDK modules, but uses the subscript loader. Either convert it to SDK code modules, or use the subscript loader yourself.
It is OK to import built-in JS Code modules in different scopes/modules. There is not actually a need to make available xpcom_generateQI from main (although it can be done; well, get to that).
To be future proof, you should bind your xpcom_generateQI shortcut properly, as in XPCOMUtils.generateQI.bind(XPCOMUtils). Otherwise, if the implementation changes and requires a proper this, your stuff will break.
To export something from any CommonJS module, you need to put it into the exports module. See the first link.
To import something, use require() (first link again).
Be aware of circular references, where Module A imports Module B imports Module A. Right now this kinda works (but only kinda, because some stuff might not be available from Module A when Module B imports it like this, as Module A is not fully loaded). Better avoid it.
Example 1 (circular)
So here is a example with circular require (main imports modules imports main)
main.js
function someFunction() {
console.log("some function called");
}
exports.someFunction = someFunction;
var mod = require("./module");
mod.anotherFunction();
module.js
const { someFunction } = require("./main");
exports.anotherFunction = function() {
someFunction();
}
Now, because of circular references this is a fragile construct. If works right now, but when modules get more complex or the SDK changes, it might break... Better put someFunction into a third module.
Example 2 (avoiding circular imports)
main.js
var mod = require("./module");
mod.anotherFunction();
// Or call someFunction directly
var { someFunction } = require("./utils");
someFunction();
module.js
const { someFunction } = require("./utils");
exports.anotherFunction = function() {
someFunction();
}
utils.js
function someFunction() {
console.log("some function called");
}
exports.someFunction = someFunction;
There are no circles anymore. If you wanted to reuse xpcom_generateQI, you'd put it as a property of exports in utils.js (in this example) and later require it with require("./utils").
https-everywhere
The https-everywhere stuff needs to be either converted or loaded using the subscript loader. I would recommend against the subscript loader, because in all likelihood the verbatim https-everywhere code does not clean up after itself. I'd actually also recommend against just converting it by throwing some stuff in (exports.xzy = ...). This code is not meant to be run in the SDK. Better create your own implementation and just borrow ideas from https-everywhere where needed.
What is the purpose of Node.js module.exports and how do you use it?
I can't seem to find any information on this, but it appears to be a rather important part of Node.js as I often see it in source code.
According to the Node.js documentation:
module
A reference to the current
module. In particular module.exports
is the same as the exports object. See
src/node.js for more information.
But this doesn't really help.
What exactly does module.exports do, and what would a simple example be?
module.exports is the object that's actually returned as the result of a require call.
The exports variable is initially set to that same object (i.e. it's a shorthand "alias"), so in the module code you would usually write something like this:
let myFunc1 = function() { ... };
let myFunc2 = function() { ... };
exports.myFunc1 = myFunc1;
exports.myFunc2 = myFunc2;
to export (or "expose") the internally scoped functions myFunc1 and myFunc2.
And in the calling code you would use:
const m = require('./mymodule');
m.myFunc1();
where the last line shows how the result of require is (usually) just a plain object whose properties may be accessed.
NB: if you overwrite exports then it will no longer refer to module.exports. So if you wish to assign a new object (or a function reference) to exports then you should also assign that new object to module.exports
It's worth noting that the name added to the exports object does not have to be the same as the module's internally scoped name for the value that you're adding, so you could have:
let myVeryLongInternalName = function() { ... };
exports.shortName = myVeryLongInternalName;
// add other objects, functions, as required
followed by:
const m = require('./mymodule');
m.shortName(); // invokes module.myVeryLongInternalName
This has already been answered but I wanted to add some clarification...
You can use both exports and module.exports to import code into your application like this:
var mycode = require('./path/to/mycode');
The basic use case you'll see (e.g. in ExpressJS example code) is that you set properties on the exports object in a .js file that you then import using require()
So in a simple counting example, you could have:
(counter.js):
var count = 1;
exports.increment = function() {
count++;
};
exports.getCount = function() {
return count;
};
... then in your application (web.js, or really any other .js file):
var counting = require('./counter.js');
console.log(counting.getCount()); // 1
counting.increment();
console.log(counting.getCount()); // 2
In simple terms, you can think of required files as functions that return a single object, and you can add properties (strings, numbers, arrays, functions, anything) to the object that's returned by setting them on exports.
Sometimes you'll want the object returned from a require() call to be a function you can call, rather than just an object with properties. In that case you need to also set module.exports, like this:
(sayhello.js):
module.exports = exports = function() {
console.log("Hello World!");
};
(app.js):
var sayHello = require('./sayhello.js');
sayHello(); // "Hello World!"
The difference between exports and module.exports is explained better in this answer here.
Note that the NodeJS module mechanism is based on CommonJS modules which are supported in many other implementations like RequireJS, but also SproutCore, CouchDB, Wakanda, OrientDB, ArangoDB, RingoJS, TeaJS, SilkJS, curl.js, or even Adobe Photoshop (via PSLib).
You can find the full list of known implementations here.
Unless your module use node specific features or module, I highly encourage you then using exports instead of module.exports which is not part of the CommonJS standard, and then mostly not supported by other implementations.
Another NodeJS specific feature is when you assign a reference to a new object to exports instead of just adding properties and methods to it like in the last example provided by Jed Watson in this thread. I would personally discourage this practice as this breaks the circular reference support of the CommonJS modules mechanism. It is then not supported by all implementations and Jed example should then be written this way (or a similar one) to provide a more universal module:
(sayhello.js):
exports.run = function() {
console.log("Hello World!");
}
(app.js):
var sayHello = require('./sayhello');
sayHello.run(); // "Hello World!"
Or using ES6 features
(sayhello.js):
Object.assign(exports, {
// Put all your public API here
sayhello() {
console.log("Hello World!");
}
});
(app.js):
const { sayHello } = require('./sayhello');
sayHello(); // "Hello World!"
PS: It looks like Appcelerator also implements CommonJS modules, but without the circular reference support (see: Appcelerator and CommonJS modules (caching and circular references))
Some few things you must take care if you assign a reference to a new object to exports and /or modules.exports:
1. All properties/methods previously attached to the original exports or module.exports are of course lost because the exported object will now reference another new one
This one is obvious, but if you add an exported method at the beginning of an existing module, be sure the native exported object is not referencing another object at the end
exports.method1 = function () {}; // exposed to the original exported object
exports.method2 = function () {}; // exposed to the original exported object
module.exports.method3 = function () {}; // exposed with method1 & method2
var otherAPI = {
// some properties and/or methods
}
exports = otherAPI; // replace the original API (works also with module.exports)
2. In case one of exports or module.exports reference a new value, they don't reference to the same object any more
exports = function AConstructor() {}; // override the original exported object
exports.method2 = function () {}; // exposed to the new exported object
// method added to the original exports object which not exposed any more
module.exports.method3 = function () {};
3. Tricky consequence. If you change the reference to both exports and module.exports, hard to say which API is exposed (it looks like module.exports wins)
// override the original exported object
module.exports = function AConstructor() {};
// try to override the original exported object
// but module.exports will be exposed instead
exports = function AnotherConstructor() {};
the module.exports property or the exports object allows a module to select what should be shared with the application
I have a video on module_export available here
When dividing your program code over multiple files, module.exports is used to publish variables and functions to the consumer of a module. The require() call in your source file is replaced with corresponding module.exports loaded from the module.
Remember when writing modules
Module loads are cached, only initial call evaluates JavaScript.
It's possible to use local variables and functions inside a module, not everything needs to be exported.
The module.exports object is also available as exports shorthand. But when returning a sole function, always use module.exports.
According to: "Modules Part 2 - Writing modules".
the refer link is like this:
exports = module.exports = function(){
//....
}
the properties of exports or module.exports ,such as functions or variables , will be exposed outside
there is something you must pay more attention : don't override exports .
why ?
because exports just the reference of module.exports , you can add the properties onto the exports ,but if you override the exports , the reference link will be broken .
good example :
exports.name = 'william';
exports.getName = function(){
console.log(this.name);
}
bad example :
exports = 'william';
exports = function(){
//...
}
If you just want to exposed only one function or variable , like this:
// test.js
var name = 'william';
module.exports = function(){
console.log(name);
}
// index.js
var test = require('./test');
test();
this module only exposed one function and the property of name is private for the outside .
There are some default or existing modules in node.js when you download and install node.js like http, sys etc.
Since they are already in node.js, when we want to use these modules we basically do like import modules, but why? because they are already present in the node.js. Importing is like taking them from node.js and putting them into your program. And then using them.
Whereas Exports is exactly the opposite, you are creating the module you want, let's say the module addition.js and putting that module into the node.js, you do it by exporting it.
Before I write anything here, remember, module.exports.additionTwo is same as exports.additionTwo
Huh, so that's the reason, we do like
exports.additionTwo = function(x)
{return x+2;};
Be careful with the path
Lets say you have created an addition.js module,
exports.additionTwo = function(x){
return x + 2;
};
When you run this on your NODE.JS command prompt:
node
var run = require('addition.js');
This will error out saying
Error: Cannot find module addition.js
This is because the node.js process is unable the addition.js since we didn't mention the path. So, we have can set the path by using NODE_PATH
set NODE_PATH = path/to/your/additon.js
Now, this should run successfully without any errors!!
One more thing, you can also run the addition.js file by not setting the NODE_PATH, back to your nodejs command prompt:
node
var run = require('./addition.js');
Since we are providing the path here by saying it's in the current directory ./ this should also run successfully.
A module encapsulates related code into a single unit of code. When creating a module, this can be interpreted as moving all related functions into a file.
Suppose there is a file Hello.js which include two functions
sayHelloInEnglish = function() {
return "Hello";
};
sayHelloInSpanish = function() {
return "Hola";
};
We write a function only when utility of the code is more than one call.
Suppose we want to increase utility of the function to a different file say World.js,in this case exporting a file comes into picture which can be obtained by module.exports.
You can just export both the function by the code given below
var anyVariable={
sayHelloInEnglish = function() {
return "Hello";
};
sayHelloInSpanish = function() {
return "Hola";
};
}
module.export=anyVariable;
Now you just need to require the file name into World.js inorder to use those functions
var world= require("./hello.js");
The intent is:
Modular programming is a software design technique that emphasizes
separating the functionality of a program into independent,
interchangeable modules, such that each contains everything necessary
to execute only one aspect of the desired functionality.
Wikipedia
I imagine it becomes difficult to write a large programs without modular / reusable code. In nodejs we can create modular programs utilising module.exports defining what we expose and compose our program with require.
Try this example:
fileLog.js
function log(string) { require('fs').appendFileSync('log.txt',string); }
module.exports = log;
stdoutLog.js
function log(string) { console.log(string); }
module.exports = log;
program.js
const log = require('./stdoutLog.js')
log('hello world!');
execute
$ node program.js
hello world!
Now try swapping ./stdoutLog.js for ./fileLog.js.
What is the purpose of a module system?
It accomplishes the following things:
Keeps our files from bloating to really big sizes. Having files with e.g. 5000 lines of code in it are usually real hard to deal with during development.
Enforces separation of concerns. Having our code split up into multiple files allows us to have appropriate file names for every file. This way we can easily identify what every module does and where to find it (assuming we made a logical directory structure which is still your responsibility).
Having modules makes it easier to find certain parts of code which makes our code more maintainable.
How does it work?
NodejS uses the CommomJS module system which works in the following manner:
If a file wants to export something it has to declare it using module.export syntax
If a file wants to import something it has to declare it using require('file') syntax
Example:
test1.js
const test2 = require('./test2'); // returns the module.exports object of a file
test2.Func1(); // logs func1
test2.Func2(); // logs func2
test2.js
module.exports.Func1 = () => {console.log('func1')};
exports.Func2 = () => {console.log('func2')};
Other useful things to know:
Modules are getting cached. When you are loading the same module in 2 different files the module only has to be loaded once. The second time a require() is called on the same module the is pulled from the cache.
Modules are loaded in synchronous. This behavior is required, if it was asynchronous we couldn't access the object retrieved from require() right away.
ECMAScript modules - 2022
From Node 14.0 ECMAScript modules are no longer experimental and you can use them instead of classic Node's CommonJS modules.
ECMAScript modules are the official standard format to package JavaScript code for reuse. Modules are defined using a variety of import and export statements.
You can define an ES module that exports a function:
// my-fun.mjs
function myFun(num) {
// do something
}
export { myFun };
Then, you can import the exported function from my-fun.mjs:
// app.mjs
import { myFun } from './my-fun.mjs';
myFun();
.mjs is the default extension for Node.js ECMAScript modules.
But you can configure the default modules extension to lookup when resolving modules using the package.json "type" field, or the --input-type flag in the CLI.
Recent versions of Node.js fully supports both ECMAScript and CommonJS modules. Moreover, it provides interoperability between them.
module.exports
ECMAScript and CommonJS modules have many differences but the most relevant difference - to this question - is that there are no more requires, no more exports, no more module.exports
In most cases, the ES module import can be used to load CommonJS modules.
If needed, a require function can be constructed within an ES module using module.createRequire().
ECMAScript modules releases history
Release
Changes
v15.3.0, v14.17.0, v12.22.0
Stabilized modules implementation
v14.13.0, v12.20.0
Support for detection of CommonJS named exports
v14.0.0, v13.14.0, v12.20.0
Remove experimental modules warning
v13.2.0, v12.17.0
Loading ECMAScript modules no longer requires a command-line flag
v12.0.0
Add support for ES modules using .js file extension via package.json "type" field
v8.5.0
Added initial ES modules implementation
You can find all the changelogs in Node.js repository
let test = function() {
return "Hello world"
};
exports.test = test;