KV on Deno Deploy - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a KV store in Deno Deploy.

Deno

const kv = await Deno.[1].open();

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

Astorage

Bkv

Cdatabase

DKV

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'kv' instead of 'KV'.

Trying to use 'storage' or 'database' which are not valid Deno properties.

The correct way to access the KV store is through Deno.KV. This opens the key-value store for use.

2fill in blank

medium

Complete the code to set a value in the KV store.

Deno

await kv.[1](['user', '123'], { name: 'Alice' });

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

Aset

Bget

Cput

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which is for reading values.

Using 'put' or 'add' which are not valid KV methods.

The set method stores a value at the given key path in the KV store.

3fill in blank

hard

Fix the error in the code to get a value from KV store.

Deno

const user = await kv.[1]('user', '123');

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

Aretrieve

Bget

Cfetch

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' which writes data instead of reading.

Passing key parts as separate arguments instead of an array.

The get method retrieves a value from the KV store. The key must be passed as an array, not separate arguments.

4fill in blank

hard

Fill both blanks to delete a key from the KV store.

Deno

await kv.[1]([[2]]);

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

Adelete

B'user', '123'

C'session', 'abc'

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' which is not a KV method.

Passing key as separate strings instead of an array.

The delete method removes a key from the KV store. The key must be passed as an array of strings.

5fill in blank

hard

Fill all three blanks to create a conditional update in KV store.

Deno

await kv.[1](['counter'], (current) => current ? current + [2] : [3]);

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

Aset

B1

C0

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' which replaces the value directly.

Using wrong numbers for increment or initial value.

The update method applies a function to the current value. It increments if exists, otherwise sets to zero.

Practice

1. What is the main purpose of KV on Deno Deploy?

easy

A. To create user interfaces

B. To run heavy computations on the server

C. To store small pieces of data in the cloud

D. To manage network connections

Solution

1. Step 1: Understand KV storage role

   KV on Deno Deploy is designed to store small data pieces like counters or preferences.

2. Step 2: Compare options with KV purpose

   Only To store small pieces of data in the cloud matches storing small data in the cloud, others describe unrelated tasks.

3. Final Answer:

   To store small pieces of data in the cloud -> Option C

4. Quick Check:

   KV stores small data = A [OK]

Hint: KV is for small cloud data storage, not heavy tasks [OK]

Common Mistakes:

• Confusing KV with computation services
• Thinking KV manages UI or network
• Assuming KV handles large files

2. Which of the following is the correct syntax to save a value '42' with key 'count' using KV in Deno Deploy?

easy

A. await kv.set('count', 42);

B. kv.set('count', 42);

C. await kv.get('count', 42);

D. kv.get('count', 42);

Solution

1. Step 1: Identify correct method to save data

   Saving data uses kv.set with await to handle the async operation.

2. Step 2: Check syntax correctness

   await kv.set('count', 42); uses await kv.set('count', 42); which is correct syntax. Options C and D use get which reads data, not saves.

3. Final Answer:

   await kv.set('count', 42); -> Option A

4. Quick Check:

   Save data = await kv.set() [OK]

Hint: Use await with kv.set to save data asynchronously [OK]

Common Mistakes:

• Omitting await causing unresolved promises
• Using kv.get instead of kv.set to save
• Passing wrong number of arguments

3. What will be the output of this code snippet on Deno Deploy KV?

const value = await kv.get('visits');
console.log(value);

Assuming 'visits' key was never set before.

medium

A. undefined

B. null

C. Throws an error

D. 0

Solution

1. Step 1: Understand kv.get behavior for missing keys

   If a key does not exist, kv.get returns null, not undefined or error.

2. Step 2: Analyze console.log output

   Since 'visits' was never set, value is null, so console.log prints null.

3. Final Answer:

   null -> Option B

4. Quick Check:

   Missing key returns null = C [OK]

Hint: Missing KV keys return null, not undefined or error [OK]

Common Mistakes:

• Expecting undefined instead of null
• Assuming kv.get throws error for missing keys
• Thinking default numeric 0 is returned

4. Identify the error in this Deno Deploy KV code snippet:

const result = kv.set('score', 100);
console.log('Score saved:', result);

medium

A. Missing await before kv.set causing unresolved promise

B. kv.set does not accept string keys

C. kv.set should be kv.save

D. console.log syntax is incorrect

Solution

1. Step 1: Check async usage of kv.set

   kv.set is asynchronous and returns a promise, so it needs await to resolve.

2. Step 2: Verify other parts of code

   Keys can be strings, kv.set is correct method, and console.log syntax is valid.

3. Final Answer:

   Missing await before kv.set causing unresolved promise -> Option A

4. Quick Check:

   Async kv.set needs await = D [OK]

Hint: Always await kv.set to avoid unresolved promises [OK]

Common Mistakes:

• Forgetting await on async kv.set
• Using wrong method name like kv.save
• Misunderstanding console.log syntax

5. You want to implement a visitor counter using KV on Deno Deploy. Which approach correctly increments the count each time a visitor arrives?

hard

A. await kv.set('visits', (await kv.get('visits')) + 1);

B. kv.set('visits', 1);

C. const current = kv.get('visits') || 0;
kv.set('visits', current + 1);

D. const current = await kv.get('visits') ?? 0;
await kv.set('visits', current + 1);

Solution

1. Step 1: Retrieve current count safely

   Use await kv.get('visits') and default to 0 if null using ?? operator.

2. Step 2: Increment and save updated count

   Add 1 to current count and await kv.set to save it asynchronously.

3. Step 3: Analyze options for correctness

   const current = await kv.get('visits') ?? 0; await kv.set('visits', current + 1); correctly handles async and null values. await kv.set('visits', (await kv.get('visits')) + 1); misses null check, C misses await, D resets count always.

4. Final Answer:

   const current = await kv.get('visits') ?? 0; await kv.set('visits', current + 1); -> Option D

5. Quick Check:

   Safe get + increment + await set = B [OK]

Hint: Use null coalescing and await both get and set [OK]

Common Mistakes:

• Not awaiting async calls
• Not handling null from kv.get
• Resetting count instead of incrementing