Reference

Objects are never copied. They are passed around by reference.

// Imagine I had a pizza
var myPizza = {slices: 5};
 // And I shared it with You
var yourPizza = myPizza;
 // I eat another slice
myPizza.slices = myPizza.slices - 1;
var numberOfSlicesLeft = yourPizza.slices;
 // Now We have 4 slices because myPizza and yourPizza
 // reference to the same pizza object.
var a = {}, b = {}, c = {};
 // a, b, and c each refer to a
 // different empty object
a = b = c = {};
 // a, b, and c all refer to
 // the same empty object