Copy javascript object without reference

js-copy-object.js

var obj = {
    a: 25, 
    b: 50, 
    c: 75,
    x: function() {
        alert(this.a);   
    }
};
var A = Object.create(obj);
var B = Object.create(obj);

A.a = 30;
B.a = 40;
B.n = 1;

alert(obj.a + " " + A.a + " " + B.a); // 25 30 40
B.x();

console.log(obj);