Redis with Node.js (ioredis) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new Redis client using ioredis.

Redis

const Redis = require('ioredis');
const redis = new [1]();

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

ARedis

Bredis

Cioredis

Dclient

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'redis' instead of 'Redis' causes an error.

Trying to use 'client' without importing it.

The Redis class from the ioredis package is used to create a new Redis client instance.

2fill in blank

medium

Complete the code to set a key 'name' with value 'Alice' in Redis.

Redis

await redis.[1]('name', 'Alice');

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

Aset

Bdel

Cget

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'set' will not store the value.

Using 'del' deletes keys, not sets them.

The set command stores a key-value pair in Redis.

3fill in blank

hard

Fix the error in the code to get the value of key 'name' from Redis.

Redis

const value = await redis.[1]('name');

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

Aset

Bdel

Cget

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' instead of 'get' causes the value to be overwritten.

Using 'del' deletes the key instead of reading it.

The get command retrieves the value stored at the given key.

4fill in blank

hard

Fill both blanks to delete the key 'name' and check if it still exists.

Redis

await redis.[1]('name');
const exists = await redis.[2]('name');

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

Adel

Bexists

Cget

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' to delete a key does not work.

Using 'set' to check existence is incorrect.

The del command deletes a key, and exists checks if the key is still present.

5fill in blank

hard

Fill all three blanks to increment a counter, get its value, and then reset it to zero.

Redis

await redis.[1]('counter');
const count = await redis.[2]('counter');
await redis.[3]('counter', 0);

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

Aincr

Bget

Cset

Ddel

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' to increment does not work.

Using 'del' instead of 'set' to reset deletes the key.

incr increases the counter by 1, get retrieves its value, and set resets it to zero.

Practice

1. What does the set method do in ioredis when used with Node.js?

easy

A. Stores a value with a specified key in Redis

B. Retrieves a value from Redis by key

C. Deletes a key-value pair from Redis

D. Connects to the Redis server

Solution

1. Step 1: Understand the purpose of set in Redis

   The set method is used to store data by assigning a value to a key in Redis.

2. Step 2: Differentiate from other methods

   get retrieves data, del deletes data, and connection is handled separately.

3. Final Answer:

   Stores a value with a specified key in Redis -> Option A

4. Quick Check:

   set stores data [OK]

Hint: Remember: set = save data, get = read data [OK]

Common Mistakes:

• Confusing set with get
• Thinking set deletes data
• Assuming set connects to Redis

2. Which of the following is the correct syntax to get a value for key 'name' using ioredis with async/await?

easy

A. const value = redis.get('name');

B. const value = redis.getSync('name');

C. const value = await redis.set('name');

D. const value = await redis.get('name');

Solution

1. Step 1: Recognize async nature of ioredis commands

   ioredis commands return promises, so await is needed to get the resolved value.

2. Step 2: Identify correct method and usage

   get retrieves the value; set stores data; getSync does not exist.

3. Final Answer:

   const value = await redis.get('name'); -> Option D

4. Quick Check:

   Use await with get [OK]

Hint: Always use await with async Redis calls [OK]

Common Mistakes:

• Omitting await causing unresolved promises
• Using non-existent getSync method
• Using set instead of get to read data

3. What will be the output of the following code snippet?

const Redis = require('ioredis');
const redis = new Redis();

async function test() {
  await redis.set('color', 'blue');
  const val = await redis.get('color');
  console.log(val);
}
test();

medium

A. null

B. undefined

C. blue

D. SyntaxError

Solution

1. Step 1: Analyze the set command

   The code stores the string 'blue' with key 'color' in Redis asynchronously.

2. Step 2: Analyze the get command and console output

   The code retrieves the value for 'color' and logs it, which should be 'blue'.

3. Final Answer:

   blue -> Option C

4. Quick Check:

   set then get returns stored value [OK]

Hint: set then get returns stored value [OK]

Common Mistakes:

• Forgetting await causing undefined output
• Assuming get returns null if key exists
• Syntax errors from missing async

4. Identify the error in the following code snippet using ioredis:

const Redis = require('ioredis');
const redis = new Redis();

function getValue() {
  const value = redis.get('key');
  console.log(value);
}
getValue();

medium

A. Missing await causing value to be a Promise

B. Incorrect Redis import statement

C. Redis client not connected

D. Using console.log inside function is invalid

Solution

1. Step 1: Understand async nature of redis.get

   The get method returns a Promise, so without await, value is a Promise object.

2. Step 2: Identify missing await and its effect

   Logging value prints a Promise, not the actual stored value.

3. Final Answer:

   Missing await causing value to be a Promise -> Option A

4. Quick Check:

   Always await async Redis calls [OK]

Hint: Always await redis.get to get actual value [OK]

Common Mistakes:

• Ignoring async/await causing Promise logs
• Thinking Redis import is wrong
• Assuming console.log inside function is invalid

5. You want to store a user's session data as a JSON object in Redis using ioredis. Which approach correctly stores and retrieves the session data?

hard

A. Store session as multiple keys like set('session:user', user) and set('session:data', data)

B. Use set('session', JSON.stringify(session)) to store and JSON.parse(await get('session')) to retrieve

C. Use hmset('session', session) without stringifying and hgetall('session') to retrieve

D. Use set('session', session) directly and await get('session') to retrieve

Solution

1. Step 1: Understand Redis stores strings

   Redis stores strings, so objects must be converted to strings before storing.

2. Step 2: Use JSON methods to store and retrieve objects

   Use JSON.stringify to convert object to string before storing, and JSON.parse to convert back after retrieving.

3. Final Answer:

   Use set('session', JSON.stringify(session)) to store and JSON.parse(await get('session')) to retrieve -> Option B

4. Quick Check:

   Stringify before set, parse after get [OK]

Hint: Stringify objects before set, parse after get [OK]

Common Mistakes:

• Trying to store objects directly without stringifying
• Using hash commands without proper structure
• Splitting session into multiple keys unnecessarily