es6(15)--generator

 //generator处理异步，下一步用next，遇到return或者yied就会停止
 {
     //generator基本定义
     let tell=function* (){
         yield 'a';
         yield 'b';
         return 'c'
     };
     let k=tell();
     console.log(k.next());
     console.log(k.next());
     console.log(k.next());
     console.log(k.next());
 }
 {
     let obj={};
     obj[Symbol.iterator]=function*(){
         yield 1;
         yield 2;
         yield 3;
     }
     for(let value of obj){
         console.log('value',value)
     }
 }
 {
     //状态机
     let state=function* (){
         while(1){
             yield 'A';
             yield 'B';
             yield 'C';
         }
     }
     let status=state();
     console.log(status.next());
     console.log(status.next());
     console.log(status.next());
     console.log(status.next());
 }
 //和上面一样，但是需要安装插件
 // {
 //     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());
 // }
 {
     //抽奖次数限制
     let draw=function(count){
         //具体逻辑
         console.info(`剩余${count}次数`)
     }

     let residue=function* (count){
         while(count>0){
             count--;
             yield draw(count);
         }
     }
     let star=residue(5);
     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)
 }
 {
     //长轮询
     let ajax=function*(){
         yield new Promise(function(resolve,reject){
             setTimeout(function(){
                 resolve({code:0})
             },1000)
         })
     }
     let pull=function(){
         let generator=ajax();
         let step=generator.next();
         step.value.then(function(d){
             if(d.code!=0){
                 setTimeout(function(){
                     console.log('wait');
                     pull()
                 },1000);
             }else{
                 console.info(d);
             }
         })
     }
     pull();
 }