es6 扩展运算符 三个点...

 es6中引入扩展运算符…，它用于把一个数组转化为用逗号分隔的参数序列，它常用在不定参数个数时的函数调用，数组合并等情形。因为typeScript是es6的超集，所以typeScript也支持扩展运算符。

1.可变参数个数的函数调用

function push(array,...items) {
array.push(...items)
}

function add(...vals){
    let sum=vals;
    return sum;
}

let arr = [1,2,3,4,5,6,7];
let sum = add(...arr);
console.log(sum);  //[1,2,3,4,5,6,7]

2.数组合并

let arr1=[1,2,3]
let arr2=[5,6]
let newarry=[88]
newarry=[2,...arr1,...arr2]
console.log(newarry) //[2, 1, 2, 3, 5, 6]

3.替代es5的apply方法

function f(x, y, z) {
// ...
}
var args = [0, 1, 2];
f(...args);

4.解构赋值

const [first, ...rest] = [1, 2, 3, 4, 5];
console.log(first) // 1
console.log(rest)// [2, 3, 4, 5]

4.转换字符串为数组

 let show=[..."hello world"]
console.log(show) //["h", "e", "l", "l", "o", " ", "w", "o", "r", "l", "d"]