LoadJS
LoadJS is a tiny async loader for modern browsers (961 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, CSS and image 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 961 bytes (minified + gzipped).
Here's an example of what you can do with LoadJS:
<script src="//unpkg.com/loadjs@latest/dist/loadjs.min.js"></script>
<script>
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');
loadjs.ready('foobar', function() {
});
</script>
You can also use more advanced syntax for more options:
<script src="//unpkg.com/loadjs@latest/dist/loadjs.min.js"></script>
<script>
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
before: function(path, scriptEl) { },
async: true,
numRetries: 3
returnPromise: false
});
loadjs.ready('foobar', {
success: function() { },
error: function(depsNotFound) { },
});
</script>
The latest version of LoadJS can be found in the dist/
directory in this repository:
It's also available from these public CDNs:
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', function() {
});
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:
Note: LoadJS treats empty CSS files as load failures in IE9-11 and uses rel="preload"
to load CSS files in Edge (to get around lack of support for onerror events on <link rel="stylesheet">
tags)
Documentation
-
Load a single file
loadjs('/path/to/foo.js', function() {
});
-
Fetch files in parallel and load them asynchronously
loadjs(['/path/to/foo.js', '/path/to/bar.js'], function() {
});
-
Fetch JavaScript, CSS and image files
loadjs(['/path/to/foo.css', '/path/to/bar.png', 'path/to/thunk.js'], function() {
});
-
Force treat file as CSS stylesheet
loadjs(['css!/path/to/cssfile.custom'], function() {
});
-
Force treat file as image
loadjs(['img!/path/to/image.custom'], function() {
});
-
Load JavaScript files as modules with non-module fallbacks (in browsers without module support)
loadjs(['module!/path/to/foo.js', 'nomodule!/path/to/bar.js'], function() {
});
-
Load a JavaScript file (only in browsers without Module support)
loadjs('nomodule!/path/to/foo.js', function() {
});
-
Add a bundle id
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', function() {
});
-
Use .ready() to define bundles and callbacks separately
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');
loadjs.ready('foobar', function() {
});
-
Use multiple bundles in .ready() dependency lists
loadjs('/path/to/foo.js', 'foo');
loadjs(['/path/to/bar1.js', '/path/to/bar2.js'], 'bar');
loadjs.ready(['foo', 'bar'], function() {
});
-
Chain .ready() together
loadjs('/path/to/foo.js', 'foo');
loadjs('/path/to/bar.js', 'bar');
loadjs
.ready('foo', function() {
})
.ready('bar', function() {
});
-
Use Promises to register callbacks
loadjs(['/path/to/foo.js', '/path/to/bar.js'], {returnPromise: true})
.then(function() { })
.catch(function(pathsNotFound) { });
-
Check if bundle has already been defined
if (!loadjs.isDefined('foobar')) {
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', function() {
});
}
-
Fetch files in parallel and load them in series
loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
success: function() { },
async: false
});
-
Add an error callback
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
success: function() { },
error: function(pathsNotFound) { }
});
-
Retry files before calling the error callback
loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
success: function() { },
error: function(pathsNotFound) { },
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) {
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;
}
});
-
Use bundle ids in error callback
loadjs('/path/to/foo.js', 'foo');
loadjs('/path/to/bar.js', 'bar');
loadjs(['/path/to/thunkor.js', '/path/to/thunky.js'], 'thunk');
loadjs.ready(['foo', 'bar', 'thunk'], {
success: function() {
},
error: function(depsNotFound) {
if (depsNotFound.indexOf('foo') > -1) {};
if (depsNotFound.indexOf('bar') > -1) {};
if (depsNotFound.indexOf('thunk') > -1) {};
}
});
-
Use .done() for more control
loadjs.ready(['dependency1', 'dependency2'], function() {
});
function fn1() {
loadjs.done('dependency1');
}
function fn2() {
loadjs.done('dependency2');
}
-
Reset dependency trackers
loadjs.reset();
-
Implement a require-like dependency manager
var bundles = {
'bundleA': ['/file1.js', '/file2.js'],
'bundleB': ['/file3.js', '/file4.js']
};
function require(bundleIds, callbackFn) {
bundleIds.forEach(function(bundleId) {
if (!loadjs.isDefined(bundleId)) loadjs(bundles[bundleId], bundleId);
});
loadjs.ready(bundleIds, callbackFn);
}
require(['bundleA'], function() { });
require(['bundleB'], function() { });
require(['bundleA', 'bundleB'], function() { });
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
-
Clone repository
$ git clone git@github.com:muicss/loadjs.git
$ cd loadjs
-
Install node dependencies using npm
$ npm install
-
Build examples
$ npm run build-examples
To view the examples you can use any static file server. To use the nodejs
http-server module:
$ npm install http-server
$ npm run http-server -- -p 3000
Then visit http://localhost:3000/examples
-
Build distribution files
$ npm run build-dist
The files will be located in the dist
directory.
-
Run tests
To run the browser tests first build the loadjs
library:
$ npm run build-tests
Then visit http://localhost:3000/test
-
Build all files
$ npm run build-all