Javascript Function Definition Syntax [duplicate]

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?

Solution 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.