A Koa middleware example

app.js

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

app.use(async (ctx, next) => {
  // Store the start time
  const start = Date.now();

  // Pass to the next middleware and wait for everything to return
  await next();

  // Calculate the total runtime everything took
  const ms = Date.now() - start;

  ctx.set('X-Response-Time', `${ms}ms`);
  console.log(`Request to ${ctx.request.url} took ${ms}ms`);
});

app.use(async (ctx, next) => {
  // Set response body (will be sent as JSON)
  ctx.body = { message: 'Hello world' };

  await next();
});

app.use(async (ctx, next) => {
  // Add the url to the response body
  ctx.body.url = ctx.request.url;
  await next();
});

app.listen(3000);