Arrays and Objects In Prototypes - Not Treated as References

Question

I have a prototype object in Javascript, when I initialise a new instance of the prototype and update properties in the prototype, it updates for all elements. I understand that

Answer 1

That's the thing: they are treated as references.

When you do this:

Test.prototype = {
    array: [], // <- This creates a new array and it's being used in all instances
    add: function (value) {
        this.array.push(value)
    }
}

What you want is getting different array instances for different class instances. In that case, simply do this.array = [] in your constructor:

let Test = function () { this.array = []; }

let Test = function () { this.array = []; }

Test.prototype = {
    array: [],
    add: function (value) {
        this.array.push(value)
    }
}

let test1 = new Test();
let test2 = new Test();

test1.add(1);
test1.add(2);

console.log(test1.array);
// => [1, 2]

console.log(test2.array);
// => []