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();
}