// 首先我們先創建一個待迭代的對象let obj = {0:'Gu',1:'Yan',2:'No.1',length:3};console.log([...obj]);// 報錯 Uncaught TypeError: obj is not iterableconsole.log(Array.from(obj));// ["Gu", "Yan", "No.1"]// 接下來我們給待迭代對象添加一個迭代器obj[Symbol.iterator] = function(){ let index = 0; let self = this; return { next(){  return {value:self[index],done:index++ === self.length} } }}console.log([...obj]) // ["Gu", "Yan", "No.1"]console.log(Array.from(obj));// ["Gu", "Yan", "No.1"]

function* guYan(){ }console.log(guYan()) // Object [Generator] {}console.log(guYan().next) // [Function: next]console.loh(guYan().next()) // { value: undefined, done: true }

function* guYan(){ yield 1, yield 2, yield 3}let it = guYan();console.log(it.next()) // { value: 1, done: false }console.log(it.next()) // { value: 2, done: false }console.log(it.next()) // { value: 3, done: false }console.log(it.next()) // { value: undefined, done: true }

obj[Symbol.iterator] = function* (){ // 每次瀏覽器都會不停的調用next方法 把yield的結果作為值 let index = 0; while(index !== this.length){ yield this[index++] }}console.log([...obj]) // ["Gu", "Yan", "No.1"]console.log(Array.from(obj));// ["Gu", "Yan", "No.1"]

function* guYan(){ let a = yield 1; console.log('a',a); let b = yield 2; console.log('b',b); let c = yield 3; console.log('c',c);}let it = guYan();//第一次調用it.next()it.next() // 什么都沒有輸出// 第二次調用it.next() // a undefined /*如果我們第二次是傳入參數調用*/it.next(100) // a 100// 第三次調用it.next(200) // b 200// 第四次調用 it.next(300) // c 300

// 實現前提 同級目錄下創建name.txt age.txt 文件；name.txt中存儲age.txt，age.txt中存儲20let fs = require('mz/fs');//我們直接使用mz包來實現fs的promise化let path = require('path');function* guYan() { let name = yield fs.readFile(path.resolve(__dirname, './name.txt'), 'utf-8'); name = yield './' + name; let age = yield fs.readFile(path.resolve(__dirname, name), 'utf-8'); return age;}let it = guYan();let { value } = it.next();value.then(data => { let { value } = it.next(data); Promise.resolve(value).then(data => {  let { value } = it.next(data)  value.then(data => {   let { value } = it.next(data);   console.log(value) // 20  }) })})

let fs = require('mz/fs');let path = require('path');function* guYan() { let name = yield fs.readFile(path.resolve(__dirname, './name.txt'), 'utf-8'); name = yield './' + name; let age = yield fs.readFile(path.resolve(__dirname, name), 'utf-8'); return age;}function co(it){ return new Promise((resolve,reject)=>{  function next(val){   let {value , done} = it.next(val);   if(done){    return resolve(value);   }   Promise.resolve(value).then(data=>{    next(data)   })  }  next(); })}co(guYan()).then(data=>{ console.log(data); // 20})

// 上述代碼可以簡化為let fs = require('mz/fs');let path = require('path');async function guYan() { let name = await fs.readFile(path.resolve(__dirname, './name.txt'), 'utf-8'); name = './' + name; let age = await fs.readFile(path.resolve(__dirname, name), 'utf-8'); return age;}// async 函數執行后返回一個promise// 可以使用try + catch ，但如果使用try + catch 返回的就是真guYan().then(data=>{ console.log(data);})