ES6 8.Generator

实例：
1.前端实现抽奖次数的限制。

{
    let draw = function (count) {
        // 具体抽奖业务逻辑
        console.log(`剩余${count}次`);
    }
    let residue = function* (count){
        while(count > 0){
            count--;
            yield draw(count);
        }
    }
    let star = residue(5); //5为后台传输进来的抽奖次数
    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);
}

2.长轮询

{
    let ajax = function* (){  //接口模拟
        yield new Promise(function(resolve,reject){
            setTimeout(function(){  //此处为项目中正常的请求数据逻辑
                resolve({code: 0});
            },200)
        })
    }

    let pull = function(){  //此段可以直接用，只需修改上方接口逻辑
        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.log(d);
            }
        })
    }
    pull();
}