16-数组的最后一位数字加1

     var arr = [3, 6, 4, 5, 1, 2, 3, 4, 5, 6, 5, 8, 2, 3, 4, 9, 9, 9]
        let num = BigInt(arr.join(''));
        // BigInt基本类型进行数学操作时，需要在数字字面量后加个n
        let string = String(num + 1n);
        let ary = string.split('');
        console.log(ary.map(str => Number(str)));