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A simple library that shims asynchronous module loading into Node.js to help with building module bundlers and client-side loaders for isomorphic apps. This library is super slim (read the source) and mainly represents an agreement between developers and users of a particular bundler/loader.

NOTE: This module is not compatible with Browserify. It is for developers that want to split their bundles for the client. For example, see dynapack.

Syntax is inspired by the CommonJS Modules/Async/A proposal.


npm install node-ensure


var ensure = require('node-ensure');
ensure(['superagent', 'react'], function(err) {
  var request = require('superagent');
  var React = require('react');
  // Do the coolest of things. 

If your bundler needs require.ensure, do this instead:

require.ensure = require('node-ensure');
require.ensure(['superagent', 'react'], function(err) {
  var request = require('superagent');
  var React = require('react');
  // Do the coolest of things. 


The returned function takes an array of strings and a callback, in that order (see the example above). The callback takes a single error argument, which usually indicates a network problem or other client-side loader-specific runtime error (it should never receive an error when used in Node.js).

Within the ensure callback, load modules with standard require calls.


This library primarily constitutes an agreement between users and developers of module bundlers and (client-side) loaders. The users agree to the usage instructions supplied above.

Bundlers and/or loaders must adhere to the following:

  • The bundler/loader uses the package.json "browser" property for replacing server-only modules with browser-ready counterparts (a la Browserify).
  • The require function passed to a module must have a require.ensure function.
  • Each require.ensure must accept the same arguments as described in Usage.
  • Each require.ensure must not access variables via closure unless those variables are shared by all require.ensure functions.
  • Each require.ensure may access properties on this. However, this assumes users have attached node-ensure to require via require.ensure = require('node-ensure').

Happy loading!