JavaScript scope gets changed? Why does this happen?

Question

The value of 'a' seems to lose global scope when the constructor a is called.

var a = 6;

function b() {
    a = 10;

    function a() {}
    console.log(a); //10
}
b();
console.log(a); //6

Answer 1

The order is interpreted as shown below due to variable hoisting. Note that as @ShadowCreeper correctly points out, function a(){} is actually creating a local variable a inside of function b which is hoisted as shown below.

var a;
var b;

a = 6;
b = function() {
 var a;
 a = function(){};
 a = 10;
 console.log(a); //10
}
b();
console.log(a); //6

Answer 2

Because you are creating a local variable (the function a) then replacing that local variable's value (the function) with 10.

One way to avoid things like this is to precede all local variables and functions with "_" (underscore).