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: 12345678,
 };

 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());
}