code: function CreateStringIterator(string) {
    CHECK_OBJECT_COERCIBLE(string, 'String.prototype[Symbol.iterator]');
    var s = TO_STRING(string);
    var iterator = new StringIterator;
    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, s);
    SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, 0);
    return iterator;
  }
docs: 21.1.5.1 CreateStringIterator Abstract Operation