[Nodejs] 20. Koa2 onion ring model ----- code demonstration

notes ： Demo official website （https://koa.bootcss.com/） The code in

1. The code is as follows ：

//  demonstration koa2  Onion ring model of middleware 

const Koa = require('koa');
const app = new Koa;

// logger ctx = req+res
app.use(async(ctx, next) => {
    
    await next();               //  Execute next Middleware 
    const rt = ctx.response.get('X-Response-Time')     // res Get time difference 
    console.log(`${
    ctx.method} ${
    ctx.url} - ${
    rt}`)
})

// x-response-time
app.use(async(ctx, next) => {
    
    const start = Date.now();
    await next();              //  Execute next Middleware 
    const ms = Date.now()- start;       //  Calculate the time difference 
    ctx.set('X-Response-Time', `${
    ms}ms`)       //  Record / Set the time difference 
})

// response
app.use(async(ctx, next) => {
    
    ctx.body = 'Hello world';
})


app.listen(3000);
console.log('koa2 Has started listening 3000 port ') 

2. Enter access in browser ：