ES6: Check if array contains an item in another array

compare_collections.js

const arr = [1,2,3];
const otherArr = [3,4,5];

arr.some(a => otherArr.some(b => a === b)); // => true

// using a collection and comparing with keys
const collection = [{a: 1}, {a: 2}, {a: 3}];
const collection2 = [{a: 3}, {a: 4}, {a: 5}];

collection.some(a => collection2.some(b => a.a === b.a)); // => true