ETag and conditional requests in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set an ETag header in the response.

Node.js

res.setHeader('ETag', [1]);

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

AcontentLength

BstatusCode

CetagValue

DrequestUrl

Attempts:

3 left

💡 Hint

Common Mistakes

Using content length or status code instead of ETag value.

The ETag header should be set to a unique value representing the resource version, here 'etagValue'.

2fill in blank

medium

Complete the code to check if the client's ETag matches the server's ETag.

Node.js

if (req.headers['if-none-match'] === [1]) {

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

AetagValue

BhostHeader

CrequestMethod

DcontentType

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with unrelated headers like content type or host.

The 'If-None-Match' header contains the client's ETag. We compare it to the server's current ETag value.

3fill in blank

hard

Fix the error in the code to send a 304 Not Modified response when ETags match.

Node.js

if (req.headers['if-none-match'] === [1]) {
  res.statusCode = 304;
  res.end();
}

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

Areq.headers['etag']

BetagValue

Cres.headers['etag']

Dreq.headers['if-match']

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong header names or response headers for comparison.

The server must compare the client's 'If-None-Match' header to the current ETag value, here 'etagValue'.

4fill in blank

hard

Fill both blanks to generate an ETag from the response body and set it in the header.

Node.js

const crypto = require('crypto');
const etag = crypto.createHash('[1]').update(body).digest('[2]');
res.setHeader('ETag', etag);

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

Asha256

Butf8

Chex

Dmd5

Attempts:

3 left

💡 Hint

Common Mistakes

Using text encodings like 'utf8' instead of digest encoding.

ETags are often generated using a hash like MD5, and the digest is commonly in hex format.

5fill in blank

hard

Fill all three blanks to handle conditional GET requests with ETag validation.

Node.js

const etag = generateETag(body);
res.setHeader('ETag', [1]);
if (req.headers['if-none-match'] === [2]) {
  res.statusCode = [3];
  res.end();
}

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

Aetag

B304

CetagValue

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for ETag header and comparison.

Responding with 200 instead of 304.

The ETag header is set to 'etag'. The request's 'If-None-Match' is compared to 'etag'. If they match, respond with 304 Not Modified.