Why does this work? Object references in Javascript

Question

I've finally been curious enough to find out why javascript does its voodoo magic to learn why not all object references are created equal.

Given the example:

var a, b, c, d;
a = 100; b = a;

c = {}; d = c;

b = 10; d.e = 'f';

console.log(a, b); // outputs 100, 10
console.log(c, d); // outputs object => e = 'f', object => e = 'f'

If all variables in javascript are objects, then what makes the use case with c and d cast explicitly as an Object so different than defining a and b as Number? Or, why will c and d be linked to one another, and not a and b?

Answer 1

All variables in JavaScript are not objects. There are native types as well.

c and d are not linked to one another. They are pointing to the same object reference. If you were to reassign d to something else, it will not affect c.

var c = {};
var d = c;
d = { foo: "bar" };

c === d // false

However, if you were to modify the object being referenced by c or d, it will modify the same object since c and d are both referring to the same object as in your example.

Answer 2

It looks to me that the difference is with b, you're reassigning the variable to a new object/value, while with d, you're modifying the existing object.