Generalized Cantor pairing function

cantor.js

const cantor = (arr) => {
  if (arr.length === 2) {
    return 1 / 2 * (arr[0] + arr[1]) * (arr[0] + arr[1] + 1) + arr[1];
  }

  return cantor(
    arr.slice(0, arr.length - 2)
      .concat(
        cantor([arr[arr.length - 1], arr[arr.length - 2]])
      )
  );
};