code: function _toIndex(it) {
  	  if (it === undefined) return 0;
  	  var number = _toInteger(it);
  	  var length = _toLength(number);
  	  if (number !== length) throw RangeError('Wrong length!');
  	  return length;
  	}
docs: https://tc39.github.io/ecma262/#sec-toindex