Server Side development with Node.js and Koa.js Quick Start Guide

Registering middleware

Registering middleware in Koa is done with the .use() method found in the application object. To register the middleware defined in the previous section:

app.use(responseTimer);

Ensure you pass in the function reference when registering the middleware, and not call the function instead. A common mistake is to pass in responseTimer() instead of responseTimer.

Next, we can define and register a middleware to send a response back for every route as shown here:

// ...app.use(async ctx => {  ctx.body = 'Hello World';});

The complete application will look like this:

// koa-middleware.js// initialize Koaconst Koa = require('koa');const app = new Koa();// create middleware functionconst responseTimer = async (ctx, next) => ...