Response time tracking middleware in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a middleware function that records the start time.

Express

function responseTimeTracker(req, res, next) {
  req.startTime = [1];
  next();
}

Drag options to blanks, or click blank then click option'

Aperformance.now()

Bnew Date().getTime()

CDate.now()

Dprocess.hrtime()

Attempts:

3 left

💡 Hint

Common Mistakes

Using process.hrtime() returns an array, not a timestamp.

Using performance.now() is not available in all Node.js versions.

We use Date.now() to get the current timestamp in milliseconds.

2fill in blank

medium

Complete the code to calculate the response time in milliseconds after the response finishes.

Express

function responseTimeTracker(req, res, next) {
  req.startTime = Date.now();
  res.on('finish', () => {
    const duration = [1] - req.startTime;
    console.log(`Response time: ${duration}ms`);
  });
  next();
}

Drag options to blanks, or click blank then click option'

Anew Date()

BDate.now()

Cperformance.now()

Dprocess.hrtime()

Attempts:

3 left

💡 Hint

Common Mistakes

Using new Date() returns a Date object, not a number.

Using process.hrtime() returns an array, not a number.

We use Date.now() again to get the current time when the response finishes, then subtract the start time.

3fill in blank

hard

Fix the error in the middleware to correctly log the response time in seconds with two decimals.

Express

function responseTimeTracker(req, res, next) {
  req.startTime = Date.now();
  res.on('finish', () => {
    const duration = (Date.now() - req.startTime) / [1];
    console.log(`Response time: ${duration.toFixed(2)}s`);
  });
  next();
}

Drag options to blanks, or click blank then click option'

A60

B10000

C100

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Dividing by 60 converts to minutes, not seconds.

Dividing by 100 or 10000 gives incorrect time units.

Dividing by 1000 converts milliseconds to seconds.

4fill in blank

hard

Fill both blanks to create a middleware that adds a custom header with the response time in milliseconds.

Express

function responseTimeTracker(req, res, next) {
  req.startTime = Date.now();
  res.on('[1]', () => {
    const duration = Date.now() - req.startTime;
    res.setHeader('[2]', duration + 'ms');
  });
  next();
}

Drag options to blanks, or click blank then click option'

Afinish

Bclose

Cresponse-time

DX-Response-Time

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'close' event may not always indicate response finished.

Using 'response-time' as header name is uncommon and may not be recognized.

The 'finish' event fires when the response is done. The header 'X-Response-Time' is a common custom header name.

5fill in blank

hard

Fill all three blanks to create a complete Express app using the response time middleware and a simple route.

Express

const express = require('express');
const app = express();

function responseTimeTracker(req, res, next) {
  req.startTime = Date.now();
  res.on('[1]', () => {
    const duration = Date.now() - req.startTime;
    res.setHeader('[2]', duration + 'ms');
  });
  next();
}

app.use([3]);

app.get('/', (req, res) => {
  res.send('Hello World');
});

app.listen(3000);

Drag options to blanks, or click blank then click option'

Afinish

BX-Response-Time

CresponseTimeTracker

Dclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'close' event instead of 'finish'.

Forgetting to pass the middleware function to app.use.

The middleware listens to the 'finish' event, sets the 'X-Response-Time' header, and is used with app.use().