Koa类构造函数设计

koa初步学习示例：

const http = require('http');
class Application {
    constructor(){
    }
    use(callback){
      this.callbackFn = callback;
    }
    listen(...args){
      const app = http.createServer(this.callbackFn);
      app.listen(...args);
    }
}
module.exports = Application;

const koa = require('./lib/application');
const app = new koa();
app.use((req, res)=>{
    res.writeHeader(500);
    res.end('Hello Simple Koa!!!!!!!');
});
app.listen(3000, ()=>{
    console.log('Simple Koa server is running...');
});

nodemon: 监听文件变化，自动重启服务。

{
  "name": "koa",
  "version": "1.0.0",
  "description": "",
  "main": "main-flow.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "server": "nodemon http-demo.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "koa": "^2.11.0"
  },
  "devDependencies": {
    "nodemon": "^2.0.4"
  }
}

请求处理流程

context对象解读
request对象解读
response对象解读

koa静态资源：
koa-static: npm i koa-static

const koa = require('koa');
const static = require('koa-static');
const app = new koa();
app.use(static(__dirname + '/public/'));
app.listen(3000);

中间件层错误处理

框架层错误处理