What I've done today is Array.diff in JavaScript.

CodeWars

Problem

Array.diff

Your goal in this kata is to implement a difference function, which subtracts one list from another and returns the result.

It should remove all values from list a, which are present in list b.

array_diff([1,2],[1]) == [2]

If a value is present in b, all of its occurrences must be removed from the other:

array_diff([1,2,2,2,3],[2]) == [1,3]

Solution

function array_diff(a, b) {
  return a.filter(e => !b.includes(e));
}

function array_diff(a, b) {
  b = new Set(b)
  return a.filter(v => !b.has(v))
}