Spread运算符
Spread运算符Spread运算符允许从 iterable 表达式（如另一个数组文本）初始化部分数组文本，或允许表达式扩展到多个参数（在函数调用中）。语法语法
var array = [[arg0ToN ,] ...iterable [, arg0ToN]]
func([args ,] ...iterable [, args | ...iterable])

var array = [[arg0ToN ,] ...iterable [, arg0ToN]]
func([args ,] ...iterable [, args | ...iterable])
参数参数iterable
必需。 迭代对象。arg0ToN
可选。 数组文本的一个或多个元素。args
可选。 函数的一个或多个参数。本文将带大家了解如何在JavaScript中使用Spread（延展操作）运算符。ES6中引入了延展操作运算符（...）。延展操作运算符将可迭代的对象扩展为其单独的元素，可迭代对象是可以使用 for 循环进行循环的任何对象。可迭代的示例：Array，String，Map，Set，DOM节点。1.在log中使用延展操作运算符1.在log中使用延展操作运算符你可以在 console.log 中对可迭代对象使用延展操作操作符
let fruits = ['', '', '', ''];
console.log(...fruits); //
let fruits = ['', '', '', ''];
console.log(...fruits); // 2.用延展操作运算符复制数组2.用延展操作运算符复制数组
let fruits = ['', '', '', ''];
let fruitsCopy = [ ...fruits ];
console.log(...fruitsCopy); //
let fruits = ['', '', '', ''];
let fruitsCopy = [ ...fruits ];
console.log(...fruitsCopy); // 复制对象
let user = {name : "John", age : 20 }
let userCopy = {...user}
let user = {name : "John", age : 20 }
let userCopy = {...user}延展操作运算符不执行深度复制。3.延展操作运算符合并3.延展操作运算符合并
let fruits = ['', '', '', ''];
let vegetables = ['', '', ''];
let fruitsAndVeg = [...fruits, ...vegetables]
let fruits = ['', '', '', ''];
let vegetables = ['', '', ''];
let fruitsAndVeg = [...fruits, ...vegetables]合并对象合并对象时，如果已经存在某个键，则将其替换为具有相同键的最后一个对象。
let user1 = {name : "John", age : 20 };
let user2 = {name : "Ram", salary: '20K' };
let userCopy = {...user1, ...user2};
userCopy ; // {name : "Ram", age :20 , salary : '20K'};
let user1 = {name : "John", age : 20 };
let user2 = {name : "Ram", salary: '20K' };
let userCopy = {...user1, ...user2};
userCopy ; // {name : "Ram", age :20 , salary : '20K'};4.延展操作运算符作为参数传递4.延展操作运算符作为参数传递
function sum(a, b) {
return a+b;
}
let num = [1,2];
sum(...num); // 3
function sum(a, b) {
return a+b;
}
let num = [1,2];
sum(...num); // 3与 math 函数一起使用
let num = [5,9,3,5,7];
Math.min(...num);
Math.max(...num);
let num = [5,9,3,5,7];
Math.min(...num);
Math.max(...num);5.延展操作运算符在解构变量中
5.延展操作运算符在解构变量中

let [melon, ...fruits ] = ['', '', '', ''];
melon; //
fruits; // [ '', '', '']

let [melon, ...fruits ] = ['', '', '', ''];
melon; //
fruits; // [ '', '', '']
解构对象
let user = {name : "Ram", age: 20, salary: '20K', job : "Tester" };
let { name, age, ...details } = user;
name; // Ram
age; // 20
details; // {salary: '20K', job : 'Tester'};
let user = {name : "Ram", age: 20, salary: '20K', job : "Tester" };
let { name, age, ...details } = user;
name; // Ram
age; // 20
details; // {salary: '20K', job : 'Tester'};6.将NodeList对象转换为数组6.将NodeList对象转换为数组NodeList类似于数组，但是没有 Array 的所有方法，例如 forEach，map，filter 等。
let nodeList = document.querySelectorAll('.class')
var nodeArray = [...nodeList]
let nodeList = document.querySelectorAll('.class')
var nodeArray = [...nodeList]7.将字符串转换为字符7.将字符串转换为字符字符串也是可迭代的对象，因此我们也可以使用 ... 来字符串。
let name = "Ram";
let chars = [...name]; // ["R", "a", "m"]

let name = "Ram";
let chars = [...name]; // ["R", "a", "m"]
8.从数组中删除重复项
let num = [1, 3, 1, 3, 3, 1];
let uniqueNum = [...new Set(num)];
uniqueNum; //[ 1, 3 ]
let num = [1, 3, 1, 3, 3, 1];
let uniqueNum = [...new Set(num)];
uniqueNum; //[ 1, 3 ]总结总结总结