const Koa = require('koa');
const app = new Koa();// x-response-timeapp.use(async (ctx) => {const start = Date.now();//await next();const ms = Date.now() - start;ctx.set('X-Response-Time', `${ms}ms`);console.log('X-Response-Time', `${ms}ms`)
});// loggerapp.use(async (ctx) => {const start = Date.now();//await next();const ms = Date.now() - start;console.log(`${ctx.method} ${ctx.url} - ${ms}`);
});// responseapp.use(async ctx => {console.log('Hello World')ctx.body = 'Hello World';
});app.listen(3000);

const Koa = require('koa');
const app = new Koa();// x-response-timeapp.use(async (ctx, next) => {const start = Date.now();
  await next();
  const ms = Date.now() - start;ctx.set('X-Response-Time', `${ms}ms`);console.log('X-Response-Time', `${ms}ms`)
});// loggerapp.use(async (ctx, next) => {const start = Date.now();
  await next();
  const ms = Date.now() - start;console.log(`${ctx.method} ${ctx.url} - ${ms}`);
});// responseapp.use(async ctx => {console.log('Hello World')ctx.body = 'Hello World';
});app.listen(3000);

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

app.use(async (ctx， next) => {const start = Date.now();
  await next();
  const ms = Date.now() - start;console.log(`${ctx.method} ${ctx.url} - ${ms}`);
});

app.listen(3000);

  use(fn) {if (typeof fn !== 'function') throw new TypeError('middleware must be a function!');if (isGeneratorFunction(fn)) {deprecate('Support for generators will be removed in v3. ' +'See the documentation for examples of how to convert old middleware ' +'https://github.com/koajs/koa/blob/master/docs/migration.md');fn = convert(fn);}debug('use %s', fn._name || fn.name || '-');this.middleware.push(fn);return this;}

  listen(...args) {debug('listen');const server = http.createServer(this.callback());return server.listen(...args);}

  callback() { const fn = compose(this.middleware);if (!this.listeners('error').length) this.on('error', this.onerror);const handleRequest = (req, res) => {res.statusCode = 404;const ctx = this.createContext(req, res);const onerror = err => ctx.onerror(err);const handleResponse = () => respond(ctx);onFinished(res, onerror);return fn(ctx).then(handleResponse).catch(onerror);};return handleRequest;}

'use strict'/*** Expose compositor.*/module.exports = compose/*** Compose `middleware` returning* a fully valid middleware comprised* of all those which are passed.** @param {Array} middleware* @return {Function}* @api public*/function compose (middleware) {if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!')for (const fn of middleware) {if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!')}/*** @param {Object} context* @return {Promise}* @api public*/return function (context, next) {// last called middleware #let index = -1
    return dispatch(0)function dispatch (i) {if (i <= index) return Promise.reject(new Error('next() called multiple times'))index = ilet fn = middleware[i]if (i === middleware.length) fn = nextif (!fn) return Promise.resolve()try {return Promise.resolve(fn(context, function next () {return dispatch(i + 1)}))} catch (err) {return Promise.reject(err)}}}
}

    if (i === middleware.length) fn = nextif (!fn) return Promise.resolve()

        return Promise.resolve(fn(context, function next () {return dispatch(i + 1)}))

fn = async (ctx, next) => {const start = Date.now();await next();const ms = Date.now() - start;ctx.set('X-Response-Time', `${ms}ms`);console.log('X-Response-Time', `${ms}ms`)
}