Javascript Array contains(val, expr)

Array.prototype.contains = (val, expr) => {
  if (!this || !this.length) return false;

  for (let i = 0; i < this.length; i++) {
    if (expr && expr(this[i], val)) return true;
    //from   ww w . ja v  a  2s  .c  om
    if (!expr && this[i] === val) return true;
  }
  return false;
};