How to check object is a Set?

Question

I'm using Set to handle my task. But when I debugged, I got

mySet.has is not a function

So my question is how to check if It's a Set. Like for the Array has Array.isArray(obj).

Answer 1

You can use instanceof

let a = new Set()
let b = [1,2]

console.log(a instanceof Set)
console.log(b instanceof Set)

On side note :-

You can also use [] instanceof Array. However, Array.isArray was created for a specific purpose: avoiding an issue with instanceof. Namely, window1.Array != window2.array; thus, new window1.Array() instanceof window2.Array == false. Same logic holds for Set. As long as you don't mess with multiple global environments, instanceof is fine. If you do, b.toString() == "[object Set]" might be better. Thanks to @andman for pointing out.

Answer 2

may be you can use instanceof.

read more here.

let s1 = new Set()
let s2 = ['a','b','c']

console.log(s1 instanceof Set)
console.log(s2 instanceof Set)

Answer 3

Another possibility for this check could be using Object.prototype.constructor:

let a = new Set([1,2]);
let b = [1,2];

console.log("a is a Set? " + (a.constructor === Set));
console.log("b is a Set? " + (b.constructor === Set));