项目中常用的ES6

摘要：看代码及注释就懂了把代码转换为代码解构赋值字符串反引号代替引号代替了正则表达式匹配数组展开符利用的实现对象对象属性有属性有值集合和添加元素，但是不会添加相同的元素，利用这个特性实现数组去重元素数量是否有指定元素删除元

看代码及注释就懂了

$ npm install -g babel-cli

$ npm install babel-preset-env --save

$ babel ./src/es6.js -w --out-file ./dist/es5.js --presets env

const breakfast = () => ["cake", "coffee", "apple"]
let [dessert, drink, fruit] = breakfast()
console.info(dessert, drink, fruit) // "cake" "coffee" "apple"

const breakfast = () => {
    return {
        dessert: "cake",
        drink: "coffee",
        fruit: "apple"
    }
}
let {dessert, drink, fruit} = breakfast()
console.info(dessert, drink, fruit) // "cake" "coffee" "apple"

反引号代替引号：`some content ${variable} some content`

str.includes()、str.startsWidth()、str.endsWith() 代替了正则表达式匹配

// 利用 Array 的 concat() 实现
let breakfast = ["cake", "coffee", "apple"]
let food = ["rice", ...breakfast]
console.info(...breakfast, food) // "cake" "coffee" "apple", ["rice", "cake", "coffee", "apple"]

// 对象属性
let food = {}
let drink = "hot drink"
food[drink] = "milk"
console.log(food["hot drink"]) // "milk"

let food = {}
let drink = "hot drink"
food[drink] = "milk"

let dessert = "cake"
food.fruit = "banane"

let breakfast = Object.assign({}, {dessert}, food) // {dessert} 有属性有值
console.log(breakfast) // {dessert: "cake", hot drink: "milk", fruit: "banane"}

let fruit = new Set(["apple", "banane", "orange"])
/* 添加元素，但是不会添加相同的元素，利用这个特性实现数组去重：[...new Set(arr)] */
fruit.add("pear")
/* 元素数量 */
console.log(fruit.size) // 4
/* 是否有指定元素 */
console.log(fruit.has("apple")) // true
/* 删除元素 */
fruit.delete("banana") 

console.log(fruit) // Set(4) {"apple", "banane", "orange", "pear"}
/* 遍历 */
fruit.forEach(item => {
    console.log(item)
})
/* 清空 */
fruit.clear()

console.log(fruit) // Set(0) {}

let food = new Map()
let fruit = {}, cook = function(){}, dessert = "甜点"
food.set(fruit, "apple")
food.set(cook, "knife")
food.set(dessert, "cake")

console.log(food, food.size) // Map(3) {{…} => "apple", ƒ => "knife", "甜点" => "cake"} 3

console.log(food.get(fruit)) // "apple"
console.log(food.get(dessert)) // "cake"

food.delete(dessert)
console.log(food.has(dessert)) // false

food.forEach((value, key) => {
    console.log(`${key} = ${value}`) // [object Object] = apple    function(){} = knife
})

food.clear()
console.log(food) // Map(0) {}

function* calc(num){
    yield num+1
    yield num-2
    yield num*3
    yield num/4
    return num
}
let cal = calc(4)
console.info(
    cal.next(), // {value: 5, done: false}
    cal.next(), // {value: 2, done: false}
    cal.next(), // {value: 12, done: false}
    cal.next(), // {value: 1, done: false}
    cal.next(), // {value: 4, done: true} 遍历完了后 done:true
    cal.next() // {value: undefined, done: true}
)

class Chef{
    constructor(food){
        this.food = food;
        this.dish = [];
    }
    get menu(){ // 不得有参数（Getter must not have any formal parameters.)
        console.log("getter 取值")
        console.log(this.dish)
        return this.dish
    }
    set menu(dish){ // 必须有一个参数（Setter must have exactly one formal parameter.）
        console.log("setter 存值")
        this.dish.push(dish)
    }
    cook(){
        console.log(this.food)
    }
}
let Gu = new Chef("vegetables");
Gu.cook() // "vegetables"
console.log(Gu.menu) // "get 取值" []

Gu.menu = "egg" // "setter 存值"
Gu.menu = "fish" // "setter 存值"

console.log(Gu.menu); // "getter 取值" ["egg", "fish"]

class Person {
    constructor(name, birth){
        this.name = name
        this.birth = birth
    }
    intro(){
        return `${this.name}的生日是${this.birth}`
    }
}

class One extends Person {
    constructor(name, birth){
        super(name, birth)
    }
}

let z = new Person("zz", "01-09")
let x = new One("xx", "01-09")

console.log(z.intro(), x.intro()) // "zz的生日是01-09" "xx的生日是01-09"
// 转化为ES5的代码大概就是
/* function Person(name, birth) {
    this.name = name;
    this.birth = birth;
}
Person.prototype.intro = function () {
    return this.name + "u7684u751Fu65E5u662F" + this.birth;
};
function One(name, birth) {
    Person.apply(this, arguments);
}
One.prototype = new Person();
var z = new Person("zz", "01-09");
var x = new One("xx", "01-09");

console.log(z.intro(), x.intro()); // "zz的生日是01-09" "xx的生日是01-09" */

回调地狱

function ajax(fn){
    setTimeout(()=>{
        console.log("执行业务")
        fn()
    },1000)
}
ajax(()=>{
    ajax(()=>{
        ajax(()=>{
            ajax(()=>{
                console.log("执行结束4")
            })
            console.log("执行结束3")
        })
        console.log("执行结束2")
    })
    console.log("执行结束1")
})
/*
    效果：
        1s： 执行业务 执行结束1
        2s:  执行业务 执行结束2
        3s： 执行业务 执行结束3
        4s:  执行业务 执行结束4
*/

Promise 这样写

function delay(word){
    return new Promise((reslove,reject) => {
        setTimeout(()=>{
            console.log("执行业务")
            reslove(word)
        },1000)
    })
}
delay("执行业务1")
    .then(word=>{
        console.log(word)
        return delay("执行业务2")
    })
    .then(word=>{
        console.log(word)
        return delay("执行业务3")
    })
    .then(word=>{
        console.log(word)
        return delay("执行业务4")
    })
    .then(word=>{
        console.log(word)
    })
    .catch()

async + await

function delay(word){
    return new Promise((reslove, reject) => {
        setTimeout(()=>{
            console.log("执行业务")
            reslove(word)
        },1000)
    })
}

const start = async () => {
    const word1 = await delay("执行业务1")
    console.log(word1)

    const word2 = await delay("执行业务2")
    console.log(word2)

    const word3 = await delay("执行业务3")
    console.log(word3)
    
    const word4 = await delay("执行业务4")
    console.log(word4)
}

start()