Question

Possible Duplicate:
Javascript: var functionName = function() {} vs function functionName() {}

Way 1:

function fancy_function(){
    // Fancy stuff happening here
}

Way 2:

var fancy_function = function(){
    // Fancy stuff happening here, too.
}

I use the former when I’m just defining a “normal” function that I’m gonna use one or several times and the latter when I’m passing it a callback for another function or so, but it looks to work fine in the both ways.

Is it really a difference in some way?

Answer 1

There is no difference to the function itself, but the latter gives you more flexibility as you have a reference to the function and it is different with regard to how it behaves if overwritten.

This allows you to achieve behaviours with the latter that you cannot achieve with the former; such as the following trick to “override” an existing function and then call the “base”:

var myOriginalFunction = function() {
    window.alert("original");
}

var original = myOriginalFunction;

var myOriginalFunction = function() {
    window.alert("overridden");
 original();
}

myOriginalFunction();

This gives you an alert “overridden”, followed by an alert “original”.

However, if you attempt this with the former notation, you’ll find you get stuck in a never ending loop of alert “overidden”.