Redefining a local variable with var in JavaScript

Question

I have a rather general question regarding JavaScript and local variables. My question is what is the difference between the following and if there is any:

function bla
{
    var a = 2;   // local variable
    a = 3;       // the local variable a gets a new value

    // Would do the following line anything different 
    // (than simply asigning this value?)
    var a = 4;
}

I suppose I won't get two local variables named a. In other languages this is even an error. So is there any use for this?

Answer 1

Any use of var within a function is hoisted. Subsequent uses on the same variable in the same scope have no effect.

It has exactly the same meaning as a = 4; alone.