...  展开运算符 (作用：数组与参数的相互转换)

用于函数调用

1.将数组转为参数

function filter1(type,x,y){

    console.log(x)//true

    console.log(y)//0

}

let items=[true, 0,false]

filter1('boolean',...items);

2.将参数或iterable转为数组

iterable是ES6标准引入的新的类型。而Array、Map和Set都属于iterable类型 

function filter1(type,...items){

    console.log(items)//  [true, 0,false] 

}

filter1('boolean',true,0,false);

例子：

1.

function push(array, ...items) { 
   // var arr =[2,3]    
   // arr.push(1,5,7)
    //console.log(arr) //[2, 3, 1, 5, 7]
     array.push(...items);  
} 

push([],4,7,9)  //[4,7,9]

2.数组自由合并(将数组转为参数)

var iterableObj = ["第一个","first"]

var arr = [...iterableObj, 4, 5, 6]

console.log(arr) // ["第一个", "first", 4, 5, 6]

function a(a,b,c,d){

    console.log(arguments)

    console.log(a)//[1, Array(2), 4]

    console.log(b)//5

    console.log(c)//6

    console.log(d)//[7]

}

var arr = [

[1,[2,3],4],

5,6,[7]

]

a(...arr)

ES5

目前为止,我们都是使用Function.prototype.apply方法来将一个数组展开成多个参数:

function myFunction(x, y, z){ }

varargs = [0,1,2];

myFunction.apply(null, args);

使用es6的展开运算符可以这么写：

function myFunction(x, y, z){ }

varargs = [0,1,2];

myFunction(...args);

选择性传参

function filterPara(type, ...items){

    console.log(items) //[false,4,'Welcome',7]

    return items.filter(item=>

        typeof item === type

    );

}

filterPara('number',false,4,'Welcome',7);// => [4, 7]

数据解构

let cold = ['autumn', 'winter','spring', 'summer'];

let otherSeasons, autumn;

[autumn, ...otherSeasons] = cold;

otherSeasons// ["winter", "spring", "summer"]

数据构造

两个对象连接返回新的对象

let a = {aa:'aa'}

let b = {bb:'bb'}

let c = {a,b}

console.log(c)  //{a: {aa:'aa'}, b: {bb:'bb'}}

let a = {aa:'aa'}

let b = {bb:'bb'}

let c = {...a,...b}

console.log(c)  // {aa: "aa", bb: "bb"}