Why caching improves performance in Express - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a cache-control header that tells browsers to cache the response for 1 hour.

Express

app.get('/data', (req, res) => {
  res.set('Cache-Control', '[1]');
  res.send('Cached data');
});

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

Apublic, max-age=3600

Bno-cache

Cno-store

Dprivate, max-age=0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'no-cache' disables caching, which hurts performance.

Setting Cache-Control to public, max-age=3600 tells browsers to cache the response for 3600 seconds (1 hour), improving performance by avoiding repeated requests.

2fill in blank

medium

Complete the code to use an in-memory cache object to store and return data if available.

Express

const cache = {};
app.get('/info', (req, res) => {
  if (cache['info']) {
    return res.send(cache['[1]']);
  }
  const data = 'Fresh info';
  cache['info'] = data;
  res.send(data);
});

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

Areq

Bdata

Cinfo

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong key like 'data' or 'cache' causes undefined results.

The cache key is 'info', so to return cached data, use cache['info']. This avoids recomputing or fetching data again, improving response time.

3fill in blank

hard

Fix the error in the middleware that caches responses by completing the missing method to send the cached data.

Express

const cache = {};
app.use((req, res, next) => {
  if (cache[req.url]) {
    return res.[1](cache[req.url]);
  }
  next();
});

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

Asend

Bwrite

Cjson

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.write() without ending the response causes hanging requests.

The res.send() method sends the cached response to the client properly. Using write or end alone won't set headers or finish the response correctly.

4fill in blank

hard

Fill both blanks to create a cache key using the request method and URL.

Express

app.use((req, res, next) => {
  const key = req.[1] + ':' + req.[2];
  if (cache[key]) {
    return res.send(cache[key]);
  }
  next();
});

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

Amethod

Burl

Cpath

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.path alone misses query parameters, causing cache misses.

Using req.method and req.url creates a unique cache key for each HTTP method and URL combination, ensuring correct cached responses.

5fill in blank

hard

Fill all three blanks to store the response data in cache and send it after the original send method.

Express

app.use((req, res, next) => {
  const key = req.method + ':' + req.url;
  const originalSend = res.[1];
  res.[2] = function (body) {
    cache[key] = body;
    return originalSend.call(this, [3]);
  };
  next();
});

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

Asend

Cbody

Dres

Attempts:

3 left

💡 Hint

Common Mistakes

Calling originalSend without .call or passing wrong argument causes errors.

We save the original res.send method in originalSend (option A). Then override res.send (option B) to cache the body (option C) before sending it. This caches responses transparently.