Javascript Function Definition Syntax [duplicate]

Question

Possible Duplicate:
JavaScript: var functionName = function() {} vs function functionName() {}
Declaring functions in JavaScript

I've seen 2 different syntaxes for defining functions in javascript:

function f() {    ... } 

As well as

var f = function() {     ... }; 

What's the difference between these? Is one of them deprecated?

Answer 1

Neither are deprecated, and both will work. The difference here is that one is a named function ( function f() ) while the other is a variable equal to a function ( var f = function() ).

You have to be careful when setting variables equal to functions. This will work:

var f = function(n) { console.log(n); }; f(3); // logs 3 

But this will break, since the variable is defined after the call to it.

f(3); // what is f? breaks. var f = function(n) { console.log(n); }; 

But normal functions work fine.

function abc(n) { console.log(n); }  abc(3); // logs 3 xyz(5); // logs 5  function xyz(n) { console.log(n); } 

This is because the code is analysed before execution, and all functions are available to call. But setting a var equal to a function is like setting a var to anything else. The order of when it happens is important.

Now for some more confusing stuff...

There are also 'self-executing' anonymous functions. They go by a variety of names. The most common way to do it looks something like this:

(function() {     // code in here will execute right away     // since the () at the end executes this (function(){}) })(); 

There is also an arguably better version.

!function() {     // again, the tailing () will execute this }(); 

Check out this Stack Overflow post for more on anonymous functions.