Find missing numbers in an array

getMissingNumbers.js

function getMissingNumbers(arr) {
  arr.sort((a, b) => (a - b));

  const min = arr[0];
  const max = arr[arr.length - 1];
  const all = [...Array(max).keys()].map(x => x + min);

  return all.filter(value => !arr.includes(value));
}

// Numbers from 100 to 1 withouth 3 and 51
const test = [...Array(100).keys()].map(x => x + 1).filter(x => (x != 51 && x != 3)).reverse()

getMissingNumbers(test); // returns [3, 51]