Checking if a Set contains a list in Javascript

Question

I have a set that I've added a list to.

var a = new Set();
a.add([1]);

Now I check if [1] exists in a:

a.has([1]);
> false

Based on the spec, this might be happening because if type is same for two objects being compared:

Return true if x and y refer to the same object. Otherwise, return false.

And this also happens:

[1] == [1]; 
> false

So it might be that the Set .has() is using == for comparing equality (not sure though). Is there a .contains() method for Set() in JS like Java has?

Answer 1

You can't compare references like arrays and objects for equality (you can compare values, though).

The way you're doing it, you're checking against a different reference, even though the values appear to be the same.

Do something like this:

var a = new Set();
var b = [1];

a.add(b);

a.has(b); // => true

Take a look at MDN's Equality comparisons and sameness.

So it might be that the Set .has() is using == for comparing equality (not sure though)

Not necessarily. [1] === [1] (using the strict equality operator) also returns false.

Is there a .contains() method for Set() in JS like Java has?

Not in the way you're imagining it. You can do some sort of deep comparison, as mentioned in the first link in this answer.

Answer 2

although both [1]'s have the same value, they are two different arrays, pointing to two different locations in memory, hence they are not equal.

you can use a basic loop to check

for (let item of mySet.keys()) {
  item.toString() == [1].toString();
  //true on match.
}