let arr = [4, 1, 6, 9, 3, 2, 8, 7];
        function compare(a, b) {
            if (a > b) return true
            else false;
        }

        function exchange(arr, a, b) {
            let temp = arr[a];
            arr[a] = arr[b];
            arr[b] = temp;
        }

        function sort(arr) {
            for (let index = 0; index < arr.length; index++) {
                for (let index = 0; index < arr.length - 1; index++) {  //减1是因为不减1 到数据最后一位的时候+ 1会超界
                    if (compare(arr[index], arr[index + 1])) {
                        exchange(arr, index, index + 1)
                    }
                }
            }

        }
        sort(arr);
        console.log(arr, 55) //[1, 2, 3, 4, 6, 7, 8, 9]