A simple function for asynchronously loading JavaScript files
JavaScript
Latest commit 75fc7db Jul 18, 2016 Scott Jehl 1.0.0

README.md

loadJS

A simple function for asynchronously loading JavaScript files

Usage

Place the loadJS function inline in the head of your page (it can also be included in an external JavaScript file if preferable).

Then call it by passing it a JavaScript URL:

<head>
...
<script>
  // include loadJS here...
  function loadJS( src ){ ... }
  // load a file with loadJS
  loadJS( "path/to/script.js" );
</script>
...
</head>

You can execute code after the Script has loaded via a callback:

<head>
...
<script>
  // include loadJS here...
  function loadJS( src ){ ... }
  // load a file with loadJS
  loadJS( "path/to/script.js", function() {
    // file has loaded
  });
</script>
...
</head>

Why not just use <script src="..." async defer>?

The async and defer attributes enjoy broad browser support. They're great options when all you need to do is load a script for all users, ideally in a non-blocking manner. The limitations with these attributes are:

  1. Some older browsers do not support async (though defer has broader support so it's typically not a problem)
  2. There's no way to use these attributes to conditionally load a script, depending on feature or environmental conditions.

Number 2 above is the main reason we use loadJS. Say you want to check if querySelector is supported before requesting your entire DOM framework and UI scripting - you'll need to use a script loader to do that. But again, if you just want to load a script unconditionally, these attributes are recommended.

Limitations

loadJS does nothing to manage execution order of requested scripts, so we do not advise using it to load multiple javascript files that depend on one another. It simply fetches a script and executes it as soon as possible. You can certainly use loadJS to load multiple scripts as long as those scripts are designed to execute independently of any other scripts being loaded by loadJS.

Contributions and bug fixes

Both are very much appreciated - especially bug fixes. As for contributions, the goals of this project are to keep things very simple and utilitarian, so if we don't accept a feature addition, it's not necessarily because it's a bad idea. It just may not meet the goals of the project. Thanks!