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
    I’m an Impostor

    This is the hardest thing I've ever had to write, much less admit to myself.  I've written resignation letters from jobs I've loved, I've ended relationships, I've failed at a host of tasks, and let myself down in my life.  All of those feelings were very...

  • By
    5 Awesome New Mozilla Technologies You’ve Never Heard Of

    My trip to Mozilla Summit 2013 was incredible.  I've spent so much time focusing on my project that I had lost sight of all of the great work Mozillians were putting out.  MozSummit provided the perfect reminder of how brilliant my colleagues are and how much...

Incredible Demos

  • By
    Image Reflection with jQuery and MooTools

    One subtle detail that can make a big difference on any web design is the use of image reflections. Using them too often can become obnoxious but using reflections on large, "masthead" images is a classy enhancement. Unfortunately creating image reflections within your...

  • By
    Introducing MooTools ScrollSidebar

    How many times are you putting together a HTML navigation block or utility block of elements that you wish could be seen everywhere on a page? I've created a solution that will seamlessly allow you to do so: ScrollSidebar. ScrollSidebar allows you...

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!