A reference implementation of a CommonJS module loader.


This is an implementation of the CommonJS module standard for a browser environment.

The kernel is a code fragment that evaluates to an unnamed function.

Modules can be loaded either synchronously and asynchronously:

  • module = require(path)
  • require(path1[, path2[, ...]], function (module1[, module2[, ...]]) {})

The kernel has the following methods:

  • define: A method for defining modules. It may be invoked one of several ways. In either case the path is expected to be fully qualified and the module a function with the signature (require, exports, module).
    • require.define(path, module)
    • require.define({path1: module1, path2: module2, path3: module3})
  • setGlobalKeyPath: A string (such as "require" and "namespace.req") that evaluates to the kernel in the global scope. Asynchronous retrieval of modules using JSONP will happen if and only if this path is defined. Default is undefined.
  • setRootURI: The URI that non-library paths will be requested relative to. Default is undefined.
  • setLibraryURI: The URI that library paths (i.e. paths that do not match /^\.{0,2}\//) will be requested relative to. Default is undefined.
  • setRequestMaximum: The maximum number of concurrent requests. Default is 2.

If a global key path was set for the kernel and the request is allowed to be asynchronous, a JSONP will be used to request the module. The callback parameter sent in the request is the define method of require (as specified by the global key path).

JSONP accomplishes CORS, so if such a request is possible to make, it is made, else, if the user agent is capable of such a request, requests to cross origin resources can be made, if not (IE[6,7]), the kernel will attempt to make a request to a mirrored location on the same origin ( becomes

Released to the public domain. In any regions where transfer the public domain is not possible the software is granted under the terms of the MIT License.