javascript - Storing arrays in ES6 Set and accessing them by value

Question

Is there a simple way to verify that an ES6 Set contains a value that is a particular array? I'd like a solution that doesn't require me to use a reference:

var set = new Set();

var array = [1, 2];
set.add(array);
set.has(array); // true

set.add([3, 4]);
set.has([3, 4]); // false

So far my solution is to store everything as a string, but this is annoying:

set.add([3, 4].toString());
set.has([3, 4].toString()); // true

Answer 1

No there is not.

A Set works on objects and primitives and is useful for preventing identical primitives and re-adding the same object instance.

Each array is their own object, so you can actually add two different arrays with the same values.

var set = new Set();
set.add([3, 4]);
set.add([3, 4]);
console.log(set.size);//2

Additionally, there's nothing to prevent an object from being changed once in a set.

var set = new Set();
var a1 = [3, 4];
var a2 = [3, 4];
set.add(a1);
set.add(a2);
a2.push(5);
for (let a of set) {
    console.log(a);
}
//Outputs:
// [3, 4]
// [3, 4, 5]

A set does not have a mechanism for checking the values of objects in a set. Since the value of an object could change at any time, it wouldn't be much more efficient than simply looping over them yourself.

The functionality you are looking has been kicked around in various ECMAScript proposals, however it does not appear to be coming anytime soon.