Immediately Executing Functions

By  on  

JavaScript is full of nifty little tricks to accomplish tasks with less code.  One of those tricks is immediately executing functions.  We oftentimes see this pattern for executing anonymous functions to limit variable scope:

(function() {
	console.log('executed!');

	// Do processing here

})();

What many developers don't know is that this code can be shorted by using a ! before the anonymous function:

!function() {
	console.log('executed!');

	// Do processing here	
}()

The function above executes immediately, just as the first snippet did.  One caveat:  the immediately executing function always returns false.  If you desire the result of the anonymous function, you wont want to use this second pattern.

Ben Alman has created an excellent, detailed writeup on the subject and if you want to learn more, be sure to visit his post!

Recent Features

  • By
    Facebook Open Graph META Tags

    It's no secret that Facebook has become a major traffic driver for all types of websites.  Nowadays even large corporations steer consumers toward their Facebook pages instead of the corporate websites directly.  And of course there are Facebook "Like" and "Recommend" widgets on every website.  One...

  • By
    Introducing MooTools Templated

    One major problem with creating UI components with the MooTools JavaScript framework is that there isn't a great way of allowing customization of template and ease of node creation. As of today, there are two ways of creating: new Element Madness The first way to create UI-driven...

Incredible Demos

  • By
    :valid, :invalid, and :required CSS Pseudo Classes

    Let's be honest, form validation with JavaScript can be a real bitch.  On a real basic level, however, it's not that bad.  HTML5 has jumped in to some extent, providing a few attributes to allow us to mark fields as required or only valid if matching...

  • By
    Scrolling “Go To Top” Link Using Dojo

    One of the most popular code snippets of posted on my blog has been the scrolling "Go To Top" link snippet. The premise of the snippet is simple: once the user scrolls an element (usually the BODY element) past a given threshold, a "Go...

Discussion

  1. Bruce Williams

    Because not quite enough people pulled out their hair on encountering the function(){…}() syntax.

  2. The first is not exactly valid. The right call has the call-parentheses inside the container parentheses.

    (function() { ... code ... }())
    

    I think the ! is works with call-parentheses too. So it’s not shorter.

    > !function(){console.log('asd')}
    false
    > !function(){console.log('asd')}()
    asd
    true
    > function(){console.log('asd')}()
    asd
    undefined
    > (function(){console.log('asd')}())
    asd
    undefined
    >
    
  3. Chris

    I think such oddities should be removed from the language.

  4. James Fishwick

    What would ever be the argument for doing this? A Obfuscated Javascript Code Contest?

  5. Why even use such a function? I don’t get it. If you want code to execute immediatly, just write it outside a ‘function’. What’s the point of an anonymous function you can’t call later on for reusability? Or am I missing something?

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!