ES8——Generator函数的使用

babel工具插件下载：npm i --save babel-polyfill
引入：polyfill.js进行转码（es8->es5）

介绍

• Generator函数用于生成迭代器
  function * (){}
  • yeild: 作用同return类似

  {const obj = function* () {yield "a";yield 123;};const fn = obj();console.log(fn.next()); // {value: 'a', done: false}console.log(fn.next()); console.log(fn.next()); // {value: undefined, done: true}
  }
  

使用场景

• 遍历对象属性

{let obj = {name: "jacak",age: 15,phone: [phone],};obj[Symbol.iterator] = function* () {for (const key of Object.keys(obj)) {yield obj[key];}};for (const val of obj) {console.log(val); // jacak 15 12345678}
}

• 保持有限个状态

{const status = function* () {while (1) {yield "success";yield "fail";yield "waiting";}};let fn = status();console.log(fn.next());console.log(fn.next());console.log(fn.next());console.log(fn.next());console.log(fn.next());
}

• 自动查询支付状态

// 查询支付状态function payState() {return new Promise((res) => {setTimeout(() => {console.log("正在查询...");res({ code: -1 });}, 1000);});}// generator迭代，获取支付状态const getPayState = function* () {yield payState();};function autoQuery() {const it = getPayState();const state = it.next();state.value.then((res) => {if (res.code == 0) {console.log("支付成功");} else {console.log("支付失败...");setTimeout(() => autoQuery(), 500);}});}autoQuery();

• 可以使异步任务按照同步顺序执行

{const ajax = function* () {console.log("任务开始");yield function (fun) {setTimeout(() => {console.log("异步任务执行");fun && fun();}, 2000);};};let fn = ajax();let sn = fn.next();sn.value(() => fn.next());
}