difference

Returns the difference between two arrays.

Create a Set from b, then use Array.prototype.filter() on a to only keep values not contained in b.

const difference = (a, b) => {
  const s = new Set(b);
  return a.filter((x) => !s.has(x));
};

difference([1, 2, 3], [1, 2, 4]); // [3]