How to calculate intersection of multiple arrays in JavaScript? And what does [equals: function] mean?

Question

I am aware of this question, simplest code for array intersection but all the solutions presume the number of arrays is two, which cannot be certain in my case.

I ha

Answer 1

Using a combination of ideas from several contributors and the latest ES6 goodness, I arrived at

const array1 = ["Lorem", "ipsum", "dolor"];
const array2 = ["Lorem", "ipsum", "quick", "brown", "foo"];
const array3 = ["Jumps", "Over", "Lazy", "Lorem"];
const array4 = [1337, 420, 666, "Lorem"];

Array.prototype.intersect = function intersect(a, ...b) {
    const c = function (a, b) {
        b = new Set(b);
        return a.filter((a) => b.has(a));
    };
    return undefined === a ? this : intersect.call(c(this, a), ...b);
};

console.log(array1.intersect(array2, array3, array4));
// ["Lorem"]