Function Literal vs Function definition

Function Literal

var Class = function () {};

vs

Function Definition

function Class () {};

the former is "hoisted" to the top of the current scope before execution. For the latter, the variable declaration is hoisted, but not the assignment. For example:

// Error, fn is called before the function is assigned!
fn();
var fn = function () { alert("test!"); } 

// Works as expected: the fn2 declaration is hoisted above the call
fn2();
function fn2() { alert("test!"); }

http://stackoverflow.com/questions/4508313/advantages-of-using-prototype-vs-defining-methods-straight-in-the-constructor