koa-heartbeat.js

// heartbeat.js
module.exports = function* heartbeat(next) {
    if (this.path !== '/heartbeat') {
        return yield next;
    }
    
    this.body = 'OK';
}

// in the index.js, we use the middleware
const app = koa();
// ...
app.use(heartbeat);
// ... more middleware, etc