扩展运算符【三点运算符】在什么场景会用到

1.复制

//数组的复制
var arr1 = ['hello']
var arr2 =[...arr1]
arr2 // ['hello']
//对象的复制
var obj1 = {name:'chuichui'}
var obj2 ={...obj1}
ob12 //  {name:'chuichui'}

2.合并

//数组的合并
var arr1 = ['hello']
var arr2 =['chuichui']
var mergeArr = [...arr1,...arr2]
mergeArr  // ['hello','chuichui']
// 对象分合并
var obj1 = {name:'chuichui'}
var obj2 = {height:176}
var mergeObj = {...obj1,...obj2}
mergeObj // {name: "chuichui", height: 176}

3.字符串转数组

var arr1 = [...'hello']
arr1 // ["h", "e", "l", "l", "o"]

4.函数传参

function f(v,w,x,y,z){ }
var args = [2,3]
f(1,...args,4,...[5])

数组中的元素迭代为函数参数时

function f(x,y,z){}
var args = [1,2,3]
f(...args)

// 以前的方法
f.apply(null,args);