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

const intersect = (arrayA, arrayB) => {
    return arrayA.filter(elem => arrayB.includes(elem));
};
const intersectAll = (...arrays) => {
    if (!Array.isArray(arrays) || arrays.length === 0) return [];
    if (arrays.length === 1) return arrays[0];
    return intersectAll(intersect(arrays[0], arrays[1]), ...arrays.slice(2));
};