LoadJS

LoadJS is a tiny async loader for modern browsers (738 bytes).

Introduction

LoadJS is a tiny async loading library for modern browsers (IE9+). It has a simple yet powerful dependency management system that lets you fetch JavaScript and CSS files in parallel and execute code after the dependencies have been met. The recommended way to use LoadJS is to include the minified source code of loadjs.js in your <html> (possibly in the <head> tag) and then use the loadjs global to manage JavaScript dependencies after pageload.

LoadJS is based on the excellent $script library by Dustin Diaz. We kept the behavior of the library the same but we re-wrote the code from scratch to add support for success/error callbacks and to optimize the library for modern browsers. LoadJS is 738 bytes (minified + gzipped).

Here's an example of what you can do with LoadJS:

// define a dependency bundle
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');

// execute code elsewhere when the bundle has loaded
loadjs.ready('foobar', {
  success: function() { /* foo.js & bar.js loaded */ },
  error: function(depsNotFound) { /* foobar bundle load failed */ }
});

The latest version of LoadJS can be found in the dist/ directory in this repository:

You can also use it as a CJS or AMD module:

$ npm install --save loadjs

var loadjs = require('loadjs');

loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');

loadjs.ready('foobar', {
  success: function() { /* foo.js & bar.js loaded */ },
  error: function(depsNotFound) {/* foobar bundle load failed */}
});

Browser Support

IE9+ (async: false support only works in IE10+)
Opera 12+
Safari 5+
Chrome
Firefox
iOS 6+
Android 4.4+

LoadJS also detects script load failures from AdBlock Plus and Ghostery in:

Safari
Chrome

Note: LoadJS treats empty CSS files as load failures in IE (to get around lack of support for onerror events on <link> tags)

Documentation

Load a single file

loadjs('/path/to/foo.js', {
  success: function() { /* foo.js loaded */}
});

Fetch files in parallel and load them asynchronously

loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
  success: function() { /* foo.js & bar.js loaded */ }
});

Fetch files in parallel and load them in series

loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
  success: function() { /* foo.js and bar.js loaded in series */ },
  async: false
});

Fetch JavaScript and CSS files

loadjs(['/path/to/foo.css', '/path/to/bar.js'], {
  success: function() { /* foo.css and bar.js loaded */ }
});

Force treating file as CSS stylesheet

loadjs(['css!/path/to/cssfile.custom'], {
  success: function() { /* cssfile.custom loaded as stylesheet */ }
});

Add a bundle id

loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
  success: function() { /* foo.js & bar.js loaded */ }
});

Check if bundle has already been defined

if (!loadjs.isDefined('foobar')) {
  loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
    success: function() { /* foo.js & bar.js loaded */ }
  });
}

Add an error callback

loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
  success: function() { /* foo.js & bar.js loaded */ },
  error: function(pathsNotFound) { /* at least one path didn't load */ }
});

Retry files before calling the error callback

loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
  success: function() { /* foo.js & bar.js loaded */ },
  error: function(pathsNotFound) { /* at least one path didn't load */ },
  numRetries: 3
});

Execute a callback before script tags are embedded

loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
  success: function() {},
  error: function(pathsNotFound) {},
  before: function(path, scriptEl) {
    /* called for each script node before being embedded */
    if (path === '/path/to/foo.js') scriptEl.crossOrigin = true;
  }
});

Bypass LoadJS default DOM insertion mechanism (DOM <head>)

loadjs(['/path/to/foo.js'], {
  success: function() {},
  error: function(pathsNotFound) {},
  before: function(path, scriptEl) {
    document.body.appendChild(scriptEl);
  
    /* return `false` to bypass default DOM insertion mechanism */
    return false;
  }
});

Execute a callback after bundle finishes loading

loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');

loadjs.ready('foobar', {
  success: function() { /* foo.js & bar.js loaded */ }
});

Chain .ready() together

loadjs('/path/to/foo.js', 'foo');
loadjs('/path/to/bar.js', 'bar');

loadjs
  .ready('foo', {
    success: function() { /* foo.js loaded */ }
  })
  .ready('bar', {
    success: function() { /* bar.js loaded */ }
  });

Compose more complex dependency lists

loadjs('/path/to/foo.js', 'foo');
loadjs('/path/to/bar.js', 'bar');
loadjs(['/path/to/thunkor.js', '/path/to/thunky.js'], 'thunk');

// wait for multiple depdendencies
loadjs.ready(['foo', 'bar', 'thunk'], {
  success: function() {
    // foo.js & bar.js & thunkor.js & thunky.js loaded
  },
  error: function(depsNotFound) {
    if (depsNotFound.indexOf('foo') > -1) {};  // foo failed
    if (depsNotFound.indexOf('bar') > -1) {};  // bar failed
    if (depsNotFound.indexOf('thunk') > -1) {};  // thunk failed
  }
});

Use .done() for more control

loadjs.ready(['dependency1', 'dependency2'], {
  success: function() {
    // run code after dependencies have been met
  }
});

function fn1() {
  loadjs.done('dependency1');
}

function fn2() {
  loadjs.done('dependency2');
}

Reset dependency trackers
```
loadjs.reset();
```

Directory structure

loadjs/
├── dist
│   ├── loadjs.js
│   ├── loadjs.min.js
│   └── loadjs.umd.js
├── examples
├── gulpfile.js
├── LICENSE.txt
├── package.json
├── README.md
├── src
│   └── loadjs.js
├── test
└── umd-templates

Development Quickstart

Install dependencies
- nodejs
- npm
- http-server (via npm)

Clone repository

$ git clone git@github.com:muicss/loadjs.git
$ cd loadjs