ES6 -- 展开运算符

展开运算符

展开运算符，将一个数组转为用逗号分隔的参数系列 ------ 更快、更便捷的操作数组

合并数组

let a = [1,2,3];
let b = [4,5,6];
let c = [...a,...b]; // [1,2,3,4,5,6]

let colors = ["red',"green","blue"]
let myColors = ["pink","orange"]
let fallColors = ["white"]

console.log([...fallColors,...myColors,...colors])//["white","pink","orange","red',"green","blue"]

// 可以向数组中插入新的元素
console.log(["skyblue",...fallColors,...myColors,...colors])//["skyblue","white","pink","orange","red',"green","blue"]

解构赋值

let a = [1,2,3,4,5,6]
let [c,...d] = a
console.log(c)  // 1
console.log(d)  // [2,3,4,5,6]
// 展开运算符必须放在最后一位

作为参数

function addNumbers(...numbers){
   return numbers.reduce((sum,number) => {
       return sum + number  
},0)  

}

console.log(addNumbers(1,2,3,4,5));   //15

浅拷贝

//数组
var a = [1,2,4]
var b = [...a]
a.push(6)
console.log(b) // [1,2,4]

//对象
var a = {a:1}
var b = {...a}
a.a = 5
console.log(b.a)  // 1

练习

function shoppingList(...items){
  if(items.indexOf('milk') < 0){
       return [milk,...items]    
  }
  return items
}

console.log(shoppingList("meat","orange","bread")) // ["milk","meat","orange","bread"]