安卓 Symbol is not defined;sdk catch error

                        //ES5
                        // for(let i=0; i<_list.length; i++){
                        //     let item = _list[i];
                        //      if (item.isCorrect) {
                        //         if (item.isCorrect) {
                        //             correctCount++;
                        //         } else {
                        //             errorCount++;
                        //         }
                        //     }
                        // }

                        //ES6
                        for (let item of _list) {
                            if (item.isCorrect) {
                                if (item.isCorrect) {
                                    correctCount++;
                                } else {
                                    errorCount++;
                                }
                            }
                        }

ES编译时报错，Symbol is not defined;sdk catch error，机型oppoR7 安卓版本4.4.4 ColorOS版本2.1