{

  // 长轮询

  let ajax=function* (){

    yield new Promise(function(resolve,reject){

      setTimeout(function () {

        resolve({code:0})

      }, 200);

    })

  }

  let pull=function(){

    let genertaor=ajax();

    let step=genertaor.next();

    step.value.then(function(d){//step.value就是promise实例

      if(d.code!=0){

        setTimeout(function () {

          console.info('wait');

          pull()

        }, 1000);

      }else{

        console.info(d);

      }

    })

  }

  pull();

}

Generator 函数是协程在 ES6 的实现，最大特点就是可以交出函数的执行权（即暂停执行）
参考链接：
http://www.ruanyifeng.com/blog/2015/04/generator.html
{

    // genertaor基本定义 有一个星号有一个yield

    let tell = function*() {

        yield 'a';

        yield 'b';

        return 'c'

    };

    let k = tell();

    console.log(k.next()); // {value: "a", done: false}

    console.log(k.next()); // {value: "b", done: false}

    console.log(k.next()); // {value: "c", done: false}

    console.log(k.next()); // {value: undefined, done: true}

}

{

    let obj = {};

    obj[Symbol.iterator] = function*() {

        yield 1;

        yield 2;

        yield 3;

    }

    for (let value of obj) {

        console.log('value', value); // 1 2 3

    }

}

{

    let state = function*() {

        while (1) {

            yield 'A';

            yield 'B';

            yield 'C';

        }

    }

    let status = state();

    console.log(status.next()); //{value: "A", done: false}

    console.log(status.next()); //{value: "B", done: false}

    console.log(status.next()); //{value: "C", done: false}

    console.log(status.next()); //{value: "A", done: false}

    console.log(status.next()); //{value: "B", done: false}

}

// {

//需要一些插件才能实现，结果跟上面一样

//   let state=async function (){

//     while(1){

//       await 'A';

//       await 'B';

//       await 'C';

//     }

//   }

//   let status=state();

//   console.log(status.next());

//   console.log(status.next());

//   console.log(status.next());

//   console.log(status.next());

//   console.log(status.next());

// }

{

    let draw = function(count) {

        //具体抽奖逻辑

        console.info(`剩余${count}次`)

    }

    let residue = function*(count) {

        while (count > 0) {

            count--;

            yield draw(count);

        }

    }

    let star = residue(5); //次数后台传

    let btn = document.createElement('button');

    btn.id = 'start';

    btn.textContent = '抽奖';

    document.body.appendChild(btn);

    document.getElementById('start').addEventListener('click', function() {

        star.next();

    }, false)

}