amd

AMD (Asynchronous Module Definition) was the response to those who thought the CommonJS Module system was not ready for the browser because its nature was synchronous.

AMD specifies a standard for modular JavaScript such that modules can load their dependencies asynchronously, solving the problems associated with synchronous loading.

Specification

Modules are defined using the define function.

define

The define function is how modules are defined with AMD. It is just a function that has this signature

define(id?: String, dependencies?: String[], factory: Function|Object);

id

Specifies the module name. It is optional.

dependencies

This argument specifies which module dependencies the module being defined has. It is an array containing module identifiers. It is optional, but if omitted, it defaults to ["require", "exports", "module"].

factory

The last argument is the one who defines the module. It can be a function (which should be called once), or an object. If the factory is a function, the value returned will be the exported value for the module.

Examples

Let's see some examples:

Named module

Defines a module named myModule that requires jQuery.

define('myModule', ['jquery'], function($) {
	// $ is the export of the jquery module.
	$('body').text('hello world');
});
// and use it
require(['myModule'], function(myModule) {});

Note: In webpack a named module is only locally available. In Require.js a named module is globally available.

Anonymous module

Define a module without specifying its id.

define(['jquery'], function($) {
	$('body').text('hello world');
});

Multiple dependencies

Define a module with multiple dependencies. Note that each dependency export will be passed to the factory function.

define(['jquery', './math.js'], function($, math) {
	// $ and math are the exports of the jquery module.
	$('body').text('hello world');
});

Export value

Define a module that exports itself.

define(['jquery'], function($) {

	var HelloWorldize = function(selector){
		$(selector).text('hello world');
	};

	return HelloWorldize;
});

Using require to load dependencies

define(function(require) {
	var $ = require('jquery');
	$('body').text('hello world');
});