Speaking JavaScript

Chapter 31. Module Systems and Package Managers

JavaScript does not have built-in support for modules, but the community has created impressive workarounds. To manage modules, you can use so-called package managers, which handle discovery, installation, dependency management, and more.

Module Systems

The two most important (and unfortunately incompatible) standards for JavaScript modules are:

CommonJS Modules (CJS)

The dominant incarnation of this standard is Node.js modules (Node.js modules have a few features that go beyond CJS). Its characteristics include:

• Compact syntax
• Designed for synchronous loading
• Main use: server

Asynchronous Module Definition (AMD)

The most popular implementation of this standard is RequireJS. Its characteristics include:

• Slightly more complicated syntax, enabling AMD to work without eval() or a static compilation step
• Designed for asynchronous loading
• Main use: browsers

Package Managers

When it comes to package managers, npm (Node Packaged Modules) is the canonical choice for Node.js. For browsers, two options are popular (among others):

• Bower is a package manager for the Web that supports both AMD and CJS.
• Browserify is a tool based on npm that compiles npm packages to something you can use in a browser.

Quick and Dirty Modules

For normal web development, you should use a module system such as RequireJS or Browserify. However, sometimes you just want to put together a quick hack. Then the following simple module pattern can help:

var moduleName ...