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umd

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UMD (Universal Module Definition) patterns for JavaScript modules that work everywhere.

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## UMD (Universal Module Definition)

[![Build Status](https://travis-ci.org/umdjs/umd.svg)](https://travis-ci.org/umdjs/umd)

This repository formalizes the design and implementation of the Universal Module Definition (UMD) API for JavaScript modules. These are modules which are capable of working everywhere, be it in the client, on the server or elsewhere.

The UMD pattern typically attempts to offer compatibility with the most popular script loaders of the day (e.g RequireJS amongst others). The repository aims to formalize the *definition* of *universal modules*. It does not provide a *universal definition*. The standard was written at the time because everyone defined their universal modules differently - there were some common approaches, with varying support for different environments, but nothing really established.

A universal module, as already noted, works in multiple environments. Before universal modules, libraries would distribute separate files for the different environments, e.g. `library.amd.js`, `library.common.js` and `library.global.js`. This was a hassle for maintainers, since it required the usage of a build tool (which JavaScript <s>does</s> did generally not need) and extra documentation. So the aim was to define a universal module, a single file, which was all that was needed for the author to write and distribute and for the user to (down)load. Notice this was before package managers and repositories were common (or: when they started to become more popular, and you had to change your library into a module to support them).

Yet, there were still variations. Modules written for web browsers did not need to consider supporting the commonjs format, as they wouldn't work in Node.JS anyway. Modules that had no dependencies wouldn't need a UMD pattern that supported `require`. Modules that did not use circular dependencies wouldn't need a pattern that supports a mutable `exports` object. You can find the explanation of these differences, and their trade-offs, in the comments documenting the patterns below. A library author can read through them and pick the right one for their supported environments.

In many cases, UMD uses [AMD](https://github.com/amdjs/amdjs-api/wiki/AMD) as a base, with special-casing added to handle [CommonJS](http://wiki.commonjs.org/wiki/CommonJS) compatibility.

### Variations

#### Regular Module

* [amdWeb.js](https://github.com/umdjs/umd/blob/master/templates/amdWeb.js) -
  Defines a module that works with AMD and browser globals. If you also want
  to export a global even when AMD is in play (useful if you are loading other
  scripts that still expect that global), use
  [amdWebGlobal.js](https://github.com/umdjs/umd/blob/master/templates/amdWebGlobal.js).
* [returnExports.js](https://github.com/umdjs/umd/blob/master/templates/returnExports.js) -
  Defines a module that works in Node, AMD and browser globals. If you also want
  to export a global even when AMD is in play (useful if you are loading other
  scripts that still expect that global), use
  [returnExportsGlobal.js](https://github.com/umdjs/umd/blob/master/templates/returnExportsGlobal.js).
* [commonjsStrict.js](https://github.com/umdjs/umd/blob/master/templates/commonjsStrict.js) -
  Defines a module that works with more CommonJS runtimes, and for modules that
  will have a circular dependency. If you also want
  to export a global even when AMD is in play (useful if you are loading other
  scripts that still expect that global), use
  [commonjsStrictGlobal.js](https://github.com/umdjs/umd/blob/master/templates/commonjsStrictGlobal.js)

#### jQuery Plugin

* [jqueryPlugin.js](https://github.com/umdjs/umd/blob/master/templates/jqueryPlugin.js) -
  Defines a jQuery plugin that works with AMD and browser globals.

#### AMD with simple Node/CommonJS adapter

These are useful for using AMD style while still making modules that can be
used in Node and installed via npm without extra dependencies to set up the
full AMD API.

This approach does not allow the use of [AMD loader plugins](https://github.com/amdjs/amdjs-api/wiki/Loader-Plugins),
just basic JS module dependencies. It also does not support the
[callback-style require](https://github.com/amdjs/amdjs-api/wiki/require) that
is usable in AMD.

* [nodeAdapter.js](https://github.com/umdjs/umd/blob/master/templates/nodeAdapter.js) -
  Best for when using AMD style but want it to work in Node without a helper library
  that sets up AMD.
* [commonjsAdapter.js](https://github.com/umdjs/umd/blob/master/templates/commonjsAdapter.js) -
  Similar to nodeAdapter.js, but compatible with more CommonJS runtimes, and if
  you want to define a circular dependency.

### Tooling

#### Build tools

* [docpad-plugin-umd](https://github.com/docpad/docpad-plugin-umd) is a [DocPad](http://docpad.org) plugin for surrounding JavaScript code with UMD boilerplate
* [grunt-umd](https://github.com/alexlawrence/grunt-umd) is a [Grunt](http://gruntjs.com) task for surrounding JavaScript code with UMD boilerplate
* [gulp-umd](https://github.com/eduardolundgren/gulp-umd) is a [Gulp](http://gulpjs.com/) task for surrounding JavaScript code with UMD boilerplate
* [grunt-urequire](https://github.com/aearly/grunt-urequire) is a Grunt wrapper for [uRequire](https://github.com/anodynos/uRequire) a conversion tool for universal JavaScript modules.
* [generator-umd](https://github.com/ruyadorno/generator-umd) is an Yeoman Generator that creates a single module project with UMD boilerplate

#### Testing

* [Unit testing UMD with grunt-contrib-jasmine](http://stackoverflow.com/questions/16940548/grunt-test-for-umd)

### Resources

* [Browserify and the Universal Module Definition](http://dontkry.com/posts/code/browserify-and-the-universal-module-definition.html)

### Todos

* noConflict. Although with AMD loaders and build tools, it should be possible to get version specific bindings,
  maybe show a version that has a noConflict option.
* Variation with attaching some functionality to a $ impersonator. Although, it is
tempting to say for that case, ask for 'jquery' as a dependency, and if the developer
wants to use something different than the actual 'jquery', map that file to the 'jquery' name.
That is one of the strengths of module names, they can be mapped to different implementations.
* Usage examples
    * Further justifications for usage
    * Gotchas/custom-tweaks we're aware of, but would rather not apply to the default UMD boilerplate

### Influences

The basic pattern for the UMD variations in this repository was derived from the approach [@kriskowal](https://github.com/kriskowal) used for the [Q promise library](https://github.com/kriskowal/q).

Earlier UMD variations were also of influence, ranging from Kit-Cambridge's
[UMD](https://gist.github.com/1251221), through to [patterns](https://github.com/addyosmani/jquery-plugin-patterns/issues/1) discussed by Addy Osmani, Thomas Davis and Ryan Florence and most recently the UMD patterns proposed by [James Burke](https://gist.github.com/1262861).

### License

Licensed under the [MIT License](https://github.com/umdjs/umd/blob/master/LICENSE.md).

umd

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