In-memory caching with node-cache in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the NodeCache library.

Express

const NodeCache = require('[1]');

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

Anode-cache

Bexpress

Ccache-node

Dmemory-cache

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'express' instead of 'node-cache'.

Mixing up package names like 'memory-cache'.

The correct package name to import is node-cache.

2fill in blank

medium

Complete the code to create a new cache instance.

Express

const cache = new NodeCache({ stdTTL: [1] });

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

A1000

B60

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting TTL to 0 disables expiration, which is not typical here.

Using a very large number like 1000 seconds without reason.

The stdTTL option sets the default time-to-live in seconds. 60 seconds is a common choice.

3fill in blank

hard

Fix the error in setting a cache value with key 'user' and value 'John'.

Express

cache.[1]('user', 'John');

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

Aget

Bput

Cadd

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'set' causes no data to be saved.

Using 'add' or 'put' which are not methods in node-cache.

The method to store a value in the cache is set.

4fill in blank

hard

Fill both blanks to retrieve a cached value and handle a cache miss.

Express

const value = cache.[1]('key');
if (value === [2]) {
  console.log('Cache miss');
}

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

Aget

Bnull

Cundefined

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for null instead of undefined causes missed cache misses.

Using 'set' instead of 'get' to retrieve data.

Use get to retrieve the value. If the key is missing, get returns undefined.

5fill in blank

hard

Fill all three blanks to create a cache, set a value, and retrieve it.

Express

const cache = new NodeCache({ stdTTL: [1] });
cache.[2]('color', 'blue');
const color = cache.[3]('color');

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

A120

Bset

Cget

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'delete' instead of 'get' to retrieve data.

Setting TTL to 0 disables expiration unintentionally.

We create a cache with TTL 120 seconds, set the key 'color' to 'blue', then get it back.

Practice

1. What is the main purpose of using node-cache in an Express app?

easy

A. To permanently save data to a database

B. To temporarily store data in memory for faster access

C. To handle user authentication securely

D. To serve static files like images and CSS

Solution

1. Step 1: Understand what caching means

   Caching means storing data temporarily to avoid repeated slow operations.

2. Step 2: Identify node-cache role in Express

   node-cache stores data in memory temporarily to speed up data retrieval.

3. Final Answer:

   To temporarily store data in memory for faster access -> Option B

4. Quick Check:

   In-memory caching = temporary fast storage [OK]

Hint: Cache stores data temporarily to speed up access [OK]

Common Mistakes:

• Confusing cache with permanent database storage
• Thinking node-cache handles authentication
• Assuming node-cache serves static files

2. Which of the following is the correct way to create a new cache instance using node-cache?

easy

A. const cache = new nodeCache();

B. const cache = nodeCache.create();

C. const cache = new NodeCache();

D. const cache = NodeCache();

Solution

1. Step 1: Recall node-cache import and usage

   node-cache is imported as NodeCache and instantiated with new keyword.

2. Step 2: Check syntax correctness

   Correct syntax is: const cache = new NodeCache();

3. Final Answer:

   const cache = new NodeCache(); -> Option C

4. Quick Check:

   Use new NodeCache() to create cache [OK]

Hint: Use 'new' keyword with NodeCache class [OK]

Common Mistakes:

• Calling nodeCache.create() which does not exist
• Using lowercase 'nodeCache' instead of 'NodeCache'
• Omitting 'new' keyword when creating instance

3. Given the code snippet below, what will be the output when accessing /data twice quickly?

const express = require('express');
const NodeCache = require('node-cache');
const app = express();
const cache = new NodeCache();

app.get('/data', (req, res) => {
  const cached = cache.get('myData');
  if (cached) {
    res.send('From cache: ' + cached);
  } else {
    const freshData = 'Hello World';
    cache.set('myData', freshData, 10);
    res.send('Fresh data: ' + freshData);
  }
});

app.listen(3000);

medium

A. First request: Fresh data: Hello World; Second request: From cache: Hello World

B. Both requests: Fresh data: Hello World

C. Both requests: From cache: Hello World

D. First request: From cache: Hello World; Second request: Fresh data: Hello World

Solution

1. Step 1: Analyze cache check on first request

   Cache is empty initially, so first request sets and returns fresh data.

2. Step 2: Analyze cache check on second request

   Second request finds data in cache and returns cached data.

3. Final Answer:

   First request: Fresh data: Hello World; Second request: From cache: Hello World -> Option A

4. Quick Check:

   Cache empty first, then hit cache second [OK]

Hint: First request sets cache, second reads from cache [OK]

Common Mistakes:

• Assuming cache is always empty
• Thinking cache returns fresh data every time
• Mixing order of fresh and cached responses

4. Identify the error in this code snippet using node-cache in Express:

const NodeCache = require('node-cache');
const cache = NodeCache();

app.get('/item', (req, res) => {
  const item = cache.get('itemKey');
  if (!item) {
    cache.set('itemKey', 'value');
    res.send('Set new item');
  } else {
    res.send('Cached item: ' + item);
  }
});

medium

A. Cache key 'itemKey' is invalid

B. Express app is not imported

C. cache.set requires a callback function

D. Missing 'new' keyword when creating cache instance

Solution

1. Step 1: Check cache instance creation

   node-cache requires 'new NodeCache()' to create an instance.

2. Step 2: Identify missing 'new' keyword

   Code uses 'NodeCache()' without 'new', causing error.

3. Final Answer:

   Missing 'new' keyword when creating cache instance -> Option D

4. Quick Check:

   Always use 'new' with NodeCache [OK]

Hint: Remember 'new' keyword for NodeCache instance [OK]

Common Mistakes:

• Forgetting 'new' keyword
• Thinking cache.set needs callback
• Assuming cache keys must be special format

5. You want to cache user profile data for 5 minutes using node-cache. Which code snippet correctly sets the cache with expiration and retrieves it safely in Express?

hard

A. cache.set('user1', profile, 300); const data = cache.get('user1'); if (data) res.send(data); else res.send('No cache');

B. cache.set('user1', profile); const data = cache.get('user1', 300); if (data) res.send(data); else res.send('No cache');

C. cache.set('user1', profile, 5); const data = cache.get('user1'); if (data) res.send(data); else res.send('No cache');

D. cache.set('user1', profile, 300000); const data = cache.get('user1'); if (data) res.send(data); else res.send('No cache');

Solution

1. Step 1: Understand TTL unit in node-cache

   TTL (time to live) is in seconds, so 5 minutes = 300 seconds.

2. Step 2: Check correct usage of set and get

   cache.set(key, value, ttl) sets with expiration; cache.get(key) retrieves value.

3. Final Answer:

   cache.set('user1', profile, 300); const data = cache.get('user1'); if (data) res.send(data); else res.send('No cache'); -> Option A

4. Quick Check:

   TTL in seconds, set with 300 for 5 minutes [OK]

Hint: TTL is seconds; 5 minutes = 300 seconds [OK]

Common Mistakes:

• Using TTL in milliseconds instead of seconds
• Passing TTL to get() method incorrectly
• Setting TTL too low (5 seconds instead of 300)