intersect.js

// Generate data

const k = 1 * 1000;

let gen = () => {
  return Array.from({length: k}, () => Math.floor(Math.random() * k));
};

let a = gen();
let b = gen();

// Intersect

function intersect(a, b) {
  return a.filter((elem) => {
    return b.indexOf(elem) > -1;
  });
}

console.log(intersect([1, 2], [1, 2, 3])); // [1, 2]

console.time("intersect");
console.log(intersect(a, b).length);
console.timeEnd("intersect");