What is the difference between these two function declarations in JavaScript? [duplicate]

Question

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

In JavaScript we can say:

function a() {};

Or we could say

var a = function() {};

Can anyone explain to me how exactly these differ, which, if any, is more preferable, and under what circumstances would one use each?

Any links or external reading would also be much appreciated.

Answer 1

One is a function declaration and one is a function expression.

http://javascriptweblog.wordpress.com/2010/07/06/function-declarations-vs-function-expressions/