Hexo
0%

ES6的剩余运算符“...”

Posted on Edited on In

...语法一般用于三种情况：

  1. ​ 对于不确定参数数量的函数
1
2
3
4
5
6
function sum(...num)
{
    return num.reduce((cur, next) => cur + next);
}
console.log(1, 2, 3);
//expected output: 6
  1. 快速创建数组, ...运算符可以将任意可枚举的对象转换为数组
1
2
3
4
5
6
7
8
9
function example()
{
    return [...arguments];
}
console.log(example(a,b,c));
//expected output: ['a','b','c']
//对string也适用
console.log([...'hello']);
//expected output: ['h','e','l','l','o'];
  1. 合并数组
1
2
3
var all = [1, ...[2,3], 4, 5];
console.log(all);
//expected output: [1,2,3,4,5]

所以，我对...运算符粗浅的看做未知数量的可迭代对象。

示例：这个代码是根据传入的字符串返回它的摩斯密码形式

使用...

1
2
3
4
5
6
7
8
9
var uniqueMorseRepresentations = function (words) {
            var mosmap = [".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..", ".---", "-.-", ".-..", "--", "-.", "---", ".--.", "--.-", ".-.", "...", "-", "..-", "...-", ".--", "-..-", "-.--", "--.."]
            var str = words.map(res => {
                var s = ''
                res.split('').map(r => {s += mosmap[r.charCodeAt() - 97]})
                return s
            })
            return [...new Set(str)].length  //就是这里看不懂
        };

未使用...

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
var uniqueMorseRepresentations = function(words) {
    const morseCode = [".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."];
  let map = {};
  let num = 0;
  let morse = '';
  for(let i = 0; i < words.length; i++) 
    {
      for(let j = 0; j < words[i].length; j++)
        {
           morse += morseCode[words[i].charCodeAt(j) - 97];
        }
      
      console.log(morse);
      if(!map[morse])
      {
        map[morse] = 1;
        num++;
      }
      morse = '';
    }
  return num;
}