What is the difference between these two functions/approaches?

Question

I use only jQuery for writing JavaScript code. One thing that confuses me is these two approaches of writing functions,

First approach

Answer 1

The function declaration syntax cannot be used within a block statement.

Legal:

function a() {
    function b() {

    }
}

Illegal:

function a() {
    if (c) {
        function b() {

        }
    }
}

You can do this though:

function a() {
    var b;
    if (c) {
        b = function() {

        };
    }
}