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Immediately Executing Functions

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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!

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Discussion

  1. Bruce Williams

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

  2. Balazs Nadasdi

    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. Andy Harvey

    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?

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