koa的执行顺序第一次看，肯定会混乱，官方文档也只是介绍了yield next的执行顺序，如果我们有自己的异步操作呢？顺序是怎样？让我们简单演示一下
var koa = require('koa');
var app = koa();
var fs = require('co-fs');
// x-response-time
app.use(function *(next){
console.log('========begin==========');
// (1) 进入路由
console.log(1)
yield next;
console.log(8);
console.log('========end==========')
});
// logger
app.use(function *(next){
console.log(2)
yield new Promise((resolve) => {
setTimeout(() => resolve(), 3000);
});
console.log(3);
yield next;
console.log(5);
let result = yield fs.readFile('./node_modules/@types/node/index.d.ts', 'utf8');
console.log(6);
result = yield new Promise((resolve) => {
setTimeout(() => resolve(), 3000);
});
console.log(7);
});
// response
app.use(function *(){
console.log(4);
this.body = 'Hello World';
});
app.listen(10000);
打开chrome浏览器，连续发送请求，观察执行顺序与结果
