Question

How to check that two variables point to the same object? Meaning that if I mutate it—the value pointed to by both variables will change. In Python there is is operator, what about JavaScript?

Answer 1

the strict equality operator (===) will evaluate to true if references are the same without doing any type conversion:

var a, b, c;
a = {};
b = {};
c = a;
console.log( a === b ); //false
console.log( a === c ); //true

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After shooting down two posts that have made the same mistakes, I think I should point out that it’s possible for == to equate a reference type with a value type due to type conversion:

var a, b;
a = {
    toString: function () {
        return 'foo';
    }
};
b = 'foo';
console.log( a == b ); //true
console.log( a === b ); //false

AFAIK if you can guarantee that both variables are reference types, == should work just fine, but that is so rarely the case that you’re better off sticking with strict comparison most of the time.