利用Generator解决异步回调原理

var i = 0;
i++;
function ajax(url){
return new Promise(function(resolve, reject){
setTimeout(function(){
console.log(url);
resolve({url: url + i++});
}, 200);
});
}function *gen(url){
var data = yield ajax(url);
data = yield ajax(data.url);
data = yield ajax(data.url);
console.log(data.url);
}function co(gen){
var iterator = gen("http://www.baidu.com");
var v = iterator.next();function step(v){
if (!v.done){
v.value.then(function(data){
step(iterator.next(data));
})
}
}step(v);
}co(gen);