JavaScript Quiz Question #2: A Set of Objects

Consider the following Set of objects spread into a new array. What gets logged?

const mySet = new Set([{ a: 1 }, { a: 1 }]);
const result = [...mySet];
console.log(result);

A) [{a: 1}, {a: 1}]
B) [{a: 1}]

Put your answer in the comments!

Comments

[Ken Bellows]

A, because separate objects are not deduped by a Set, even if they happen to have an identical structure and values. If you wanted it to log B, you'd have to do this:

const o = {a: 1}
const mySet = new Set([o, o])
const result = [...mySet]
console.log(result)

Here the object does get deduped because it's the same exact object instance twice, not two different object instances that looks the same.

[moth]

A!

This is because in JS Objects are passed by reference instead of value.

Just for fun, one of my first packages on npm was to make a superset of Set that included functionality allows you to do this by reference.

npmjs.com/package/spicy-set

[Andrei Voicu]

B

[Huynh HD]

A