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Create external Browserify bundles for lazy asynchronous loading

Introduction to asynchronous module loading with Browserify:


npm install externalize


The module exports a single function

    <parent bundle or array of parent bundles>,
    <bundle or arrays of bundles to be externalized from the parent bundles>,
    <callback fucntion>


Create two bundles where the second one is a subset of the parent and call externalize(parent, subset, callback) on them. It will do following:

  1. Moves all modules that are used in both to the parent one
  2. Removes those modules from the parent one that are explicitly requireable in the subset one
  3. It generally tries to do the "right thing"

in code:

var fs = require("fs");
var browserify = require("browserify");
var externalize = require("externalize");
// Parent bundle with an entry point 
var parent = browserify("./index.js");
// Make subset bundle from external.js by making it explicitly requireable 
var subset = browserify().require("./external.js");
// Remove the subset bundle code from the parent 
externalize(parent, subset, function(err) {
    if (err) throw err;
    // Write bundles to files after externalization 


// require("./external"); 
// Would not work here because external.js is externalized to the subset bundle 
// Use any script loader to load the subset bundle to make the require work 
// again 
jQuery.getScript("bundle/subset.js", function(){
    var value = require("./external");
    // Alerts: "external module: external module contents" 
    alert("external module: " + value);


module.exports = "external module contents";

Script loaders

You need a script loader to load the external bundles. There is one in jQuery. If you don't use jQuery you can grab $script.js from npm or implement your own for modern browsers easily.

Some others include: