Contextual-execution Javascript snippet. Fires a callback when it finds a given classname.
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Contexe - Contextual Executor

Contexe is a tiny, tiny snippet that provides an easy way to run code when a particular class attribute is present on either the body or html tag. It's essentially a simplified version of the Garber-Irish method.

What for?

In CSS, you can easily give custom styles to a particular page while delivering the same CSS file to all pages:

/* To communicate our brand values, make the intro text "pop" on the home page */
body.home .intro {
  color: red;
  font: bold italic xx-large "Comic Sans";
  text-decoration: blink;

In fact, some Content-management systems make this extra-easy by auto-generating classes based on context (in WordPress, body_class() will do the trick). I wanted a way to do the same sort of thing in Javascript: deliver one Javascript file and fire parts of it based on a classname.

How to use it

Include the Contexe snippet in your own file, or link to it with a script tag.

<script src="/path/to/contexe.js"></script>

Create a new Contexe instance, give it the tag you want to test against:

var exe = new Contexe('html');

exe.given('my-context-class', function() {
  // Do something

Too much typing? Do it the lazy way:

Contexe('body').given('my-context-class', function() {});

Chain given's together:

  .given('ted', function(){ console.log('Alright!') })
  .given('bill', function(){ console.log('Shut up, Ted!')  });

Apply arguments to your callback:

var totally = function (adj) {
  console.log('Totally ' + adj + '!');
  .given('awesome', totally, ['awesome']); // "Totally awesome!"
  .given('lame', totally, ['lame']); // "Totally lame!"

Technical things


Contexe can take three values:

  • 'html': which will cause it to check the html element for that instance
  • 'body': which will cause it to check the body element
  • A DOM Element: I don't know why you would want to do this, but you can

If you don't use the "new" keyword, Contexe will create a new instance automatically and memoize it. If Contexe is called again later using the same argument, it'll return the instance that was memoized.

If you're going to use 'body' or a DOM element, make sure you create your Contexe instance on or after DOMReady!


Takes three arguments: classname, callback and arguments as an array.


Want something more... MVC? Try the Garber-Irish method!