Removes the last element from the array and returns it. See ECMA-262, section 15.4.4.6.
function ArrayPop() {
  CHECK_OBJECT_COERCIBLE(this, "Array.prototype.pop");

  var array = TO_OBJECT(this);
  var n = TO_LENGTH(array.length);
  if (n == 0) {
    array.length = n;
    return;
  }

  n--;
  var value = array[n];
  %DeleteProperty_Strict(array, n);
  array.length = n;
  return value;
}