"Variables" are just name tags, they can point to the same object, like in JS:

var a = [];
var b = a; // a and b are the same object
a.push(1); // both a and b are [1] now

If you want to work with them you need to copy every object (read: anything that's not a primitive value):

var a = [];
var c = a.slice(); // c is a shallow copy of a, so different object
a.push(1); // c remains []