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JavaScript Universal Module Definition (UMD)


The UMD (Universal Module Definition) pattern is used when our module needs to be imported by a number of different module loaders (e.g. AMD, CommonJS).

The pattern itself consists of two parts:

  1. An IIFE (Immediately-Invoked Function Expression) that checks for the module loader that is being implemented by the user. This will take two arguments; root (a this reference to the global scope) and factory (the function where we declare our module).

  2. An anonymous function that creates our module. This is passed as the second argument to the IIFE portion of the pattern. This function is passed any number of arguments to specify the dependencies of the module.

In the below example we check for AMD, then CommonJS. If neither of those loaders are in use we fall back to making the module and its dependencies available globally.

(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as an anonymous module.
        define(['exports', 'b'], factory);
    } else if (typeof exports === 'object' && typeof exports.nodeName !== 'string') {
        // CommonJS
        factory(exports, require('b'));
    } else {
        // Browser globals
        factory((root.commonJsStrict = {}), root.b);
}(this, function (exports, b) {
    //use b in some fashion.

    // attach properties to the exports object to define
    // the exported module properties.
    exports.action = function () {};