ES6的准备==>koa

迭代器

function makeIteeator(arr) {
    let nextIndex = 0;
    //返回一个迭代器对象
    return {
        next: () => {
            //next()方法返回的对象结果
            if (nextIndex < arr.length) {
                return {
                    value: arr[nextIndex++],
                    done: true
                }
            } else {
                return { done: true }
            }
        }
    }
}
const it = makeIteeator(['吃饭', '睡觉', '打豆豆'])
console.log('首先', it.next().value)
console.log('其次', it.next().value)
console.log('然后', it.next().value)
console.log('最后', it.next().value)

生成器函数

function* makeIterator(arr) {
    for (let i = 0; i < arr.length; i++) {
        yield arr[i]
    }
}
const gen = makeIterator(['吃饭', '睡觉', '打豆豆'])
console.log('首先', gen.next().value)
console.log('其次', gen.next().value)
console.log('然后', gen.next().value)
console.log('最后', gen.next().done)

图片.png

co库(源码)

const co = require('co');
const fetch = require('node-fetch');
co(function*() {
    const res = yield fetch('https://api.douban.com/v2/movie/1291843')
    const movie = yield res.json()
    const summary = movie.summary
    console.log('summary', summary)
})

//上面的执行过程
function run(generator) {
    const iterator = generator()
    const it = iterator.next()
    const promise = it.value
    promise.then(data => {
        const it2 = iterator.next(data)
        const promise2 = it2.value

        promise2.then(data2 => {
            iterator.next(data2)
        })
    })
}

箭头函数

写法精简
和定义父作用域共享this
用法示例

const arrow = function(param){}
const arrow = (param)=>{}
const arrow=param=>{}
const arrow =param=>console.log(param)
const arrow = param=({param:param})
const arrow = (param1,param2)=>{}
const arrow=({id,movie})=>{
    console.log(id,movie)
}

处理异步的场景

const fs = require('fs')
    //第一阶段回调函数
function readFile(cb) {
    fs.readFile('./package.json', (err, data) => {
        if (err) return console.log(err)
        data = JSON.parse(data)
        cb(null, data)

    })
}
readFile((err, data) => {
        if (!err) {
            data.JSON.parse(data)
            console.log(data.name)
        }
    })
    //第二阶段promise
function readFileAsync(path) {
    return new Promise((resolve, reject) => {
        fs.readFile(path, (err, data) => {
            if (err) reject(err)
            else resolve(data)
        })
    })
}
readFileAsync('./package.json')
    .then(data => {
        data = JSON.parse(data)
        console.log(data.name)
    })
    //第三阶段

const co = require('co');
const util = require('util')
co(function*() {
        let data = yield util.promisify(fs.readFile)('./package.json')
        data = JSON.parse(data)
        console.log(data.name)
    })
    //第四阶段Async统一事件
const readAsync = util.promisify(fs.readFile)
async function init() {
    let data = await readAsync('./package.json')
    data = JSON.parse(data)
    console.log(data.name)
}
init()

import export

babel生产环境