1）数组合并
[1, 2, ...[3], ...[4, 5]] 返回[1, 2, 3, 4, 5]
2）与解构赋值结合
[first, ...more] = [1, 2, 3, 4, 5] // first = [1], more = [2, 3, 4, 5]
3）函数返回多个值
4）32位unicode字符串的正确长度计算