Compression middleware in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output behavior of this Express app using compression middleware?

Consider this Express.js server code snippet using compression middleware:

import express from 'express';
import compression from 'compression';

const app = express();
app.use(compression());

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

app.listen(3000);

What happens when a client sends a request with Accept-Encoding: gzip header?

Node.js

import express from 'express';
import compression from 'compression';

const app = express();
app.use(compression());

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

app.listen(3000);

A The server responds with compressed content but does not set any Content-Encoding header.

B The server responds with uncompressed 'Hello World!' ignoring the Accept-Encoding header.

C The server throws an error because compression middleware requires manual compression calls.

D The server responds with compressed (gzip) 'Hello World!' content and sets 'Content-Encoding: gzip' header.

💡 Hint

Compression middleware automatically compresses responses when the client supports it.

The compression middleware checks the client's Accept-Encoding header and compresses the response accordingly. It also sets the Content-Encoding header to inform the client about the compression type.

📝 Syntax

intermediate

Which option correctly applies compression middleware only to JSON responses?

You want to compress only JSON responses in your Express app. Which code snippet correctly achieves this?

A app.use(compression({ filter: (req, res) => res.getHeader('Content-Type') === 'application/json' }));

B app.use(compression({ filter: (req, res) => res.getHeader('content-type')?.includes('application/json') }));

C app.use(compression({ filter: (req, res) => req.headers['content-type'] === 'application/json' }));

D app.use(compression({ filter: (req, res) => res.headers['Content-Type'] === 'application/json' }));

💡 Hint

Headers are case-insensitive and may include charset info.

The filter option receives req and res. The response header content-type may include charset, so checking with includes is safer. Header names are lowercase in Node.js.

🔧 Debug

advanced

Why does this Express app fail to compress responses?

Look at this Express app code:

import express from 'express';
import compression from 'compression';

const app = express();

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

app.use(compression());

app.listen(3000);

Why are responses not compressed?

Node.js

import express from 'express';
import compression from 'compression';

const app = express();

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

app.use(compression());

app.listen(3000);

A Compression middleware is added after routes, so it does not affect responses.

B Compression middleware only works with POST requests.

C The app is missing a call to next() in the route handler.

D Compression middleware requires manual calls to compress responses.

💡 Hint

Middleware order matters in Express.

Middleware in Express runs in the order it is added. Adding compression after routes means it never runs before sending the response, so no compression happens.

🧠 Conceptual

advanced

What is the main benefit of using compression middleware in a Node.js server?

Why do developers add compression middleware like compression in their Node.js servers?

A To reduce the size of response bodies, improving load times and saving bandwidth.

B To encrypt response data for security purposes.

C To cache responses on the server for faster repeated requests.

D To convert all responses to JSON format automatically.

💡 Hint

Think about what compression means in everyday life.

Compression reduces the size of data sent over the network, making pages load faster and using less bandwidth.

❓ state_output

expert

What is the Content-Encoding header value after this code runs?

Given this Express app snippet:

import express from 'express';
import compression from 'compression';

const app = express();
app.use(compression({ threshold: 1024 }));

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

app.listen(3000);

If a client requests '/' with Accept-Encoding: gzip, what is the Content-Encoding header in the response?

Node.js

import express from 'express';
import compression from 'compression';

const app = express();
app.use(compression({ threshold: 1024 }));

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

app.listen(3000);

A Content-Encoding: br (Brotli) is set automatically.

B Content-Encoding: deflate is set by default.

C No Content-Encoding header is set because response size is below threshold.

D Content-Encoding: gzip is set because client accepts gzip.

💡 Hint

Check the meaning of the threshold option in compression middleware.

The threshold option sets the minimum response size (in bytes) to compress. Since 'Short' is less than 1024 bytes, compression is skipped and no Content-Encoding header is set.