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Immediately-Invoked Function Expression (IIFE)

Module by: Hannes Hirzel. E-mail the author

Summary: In this module it is explained what an IIFE (Immediately invoked function expression) is in JavaScript and what it is used for. An application example is given.

Introduction

When reading JavaScript code you often see expressions which look quite arcane: 



(function () {
	// variable declarations here
	// JavaScript code (has access to all globals)
}());
Alternatively it could be 


(function () {
	// variable declarations here
	// JavaScript code (has access to all globals)
})();
If you take the second variant apart and simplify it you see 


(..function expression...)();
It is a definition of an anonymous function which is invoked right after it has been defined.

Application

Initialisation

An immediately invoked anonymous function may be used for initialization code. There are variables needed to set up the environment which afterwards are no longer used and should not clutter the name space.

Comments

The IIFE related to the namespace pattern which is used to avoid defining too many global variables.

Using an immediately invoked function has the same effect as 



function myFunc(){
    // do things
}
myFunc();
The only difference is that myFunc is not added to the global name space. This is fine if the function is only used once.

References

Ben Alman explains why Immediately-invoked function expression is a better term than self-executing anonymous function or self-invoked anonymous function which is used as well.

Addy Osmany, Essential JavaScript Namespacing (point 4)

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