Why does changing one array alters the other?

Question

Consider this tiny bit of javascript code:

var a = [1, 2, 3],
    b = a;

b[1] = 3;

a; // a === [1, 3, 3] wtf!?

Why does \"a\" change when

Answer 1

Assigning an array does not create a new array, it's just a reference to the same array. Numbers and booleans are copied when assigned to a new variable.

Answer 2

It's the same array (since it's an object, it's the same reference), you need to create a copy to manipulate them separately using .slice() (which creates a new array with the elements at the first level copied over), like this:

var a = [1, 2, 3],
    b = a.slice();

b[1] = 3;

a; // a === [1, 2, 3]