RequireJS

RequireJS is a JavaScript file and module loader that implements the Asynchronous Module Definition (AMD) API. It is designed to load JavaScript modules asynchronously in the browser, manage dependencies, and minimize code that runs before it is ready. By using AMD, modules declare their dependencies and are executed in the correct order once loaded, helping to avoid global namespace pollution.

In practice, modules are defined with define([dependencies], factory) and loaded with require([dependencies], callback). A loader script, typically require.js, is included in the page, and a main module can be specified with a data-main attribute. The loader fetches modules via HTTP as needed, enabling parallel loading and on-demand execution. It also supports configuration to tailor the loading behavior.

Key features include configuration of paths to map module names to URLs, shim to integrate non-AMD scripts by specifying their exported global, and bundles for production to reduce requests. It supports plugins, enabling loading of resources beyond JavaScript, such as text, JSON, or CSS, through plugin syntax.

A production workflow often uses the r.js optimizer to bundle and minify modules into a single file, improving load performance in production environments. RequireJS influenced the JavaScript module ecosystem and remains a reference implementation for AMD, with the loader and its ecosystem supporting modular development across many projects. The project is released under a permissive open-source license and has contributed to broader discussions about browser-based module loading and dependency management.