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

Small recursive divide and conquer solution that does not rely on es6 or any library.

It accepts an array of arrays which makes the code shorter and allows you to pass arguments by using map.

function intersection(a) {
    if (a.length > 2)
        return intersection([intersection(a.slice(0, a.length / 2)), intersection(a.slice(a.length / 2))]);

    if (a.length == 1)
        return a[0];

    return a[0].filter(function(item) {
        return a[1].indexOf(item) !== -1;
    });
}

var list1 = [ 'a', 'b', 'c' ];
var list2 = [ 'd', 'b', 'e' ];
var list3 = [ 'f', 'b', 'e' ];
console.log(intersection([list1, list2, list3]));