Deno KV (built-in key-value store) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open the Deno KV store.

Deno

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

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

AopenKv

Bconnect

Copen

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'open' instead of 'openKv' causes an error.

Trying to use synchronous methods instead of async.

The method openKv() is used to open the Deno KV store asynchronously.

2fill in blank

medium

Complete the code to set a key-value pair in the KV store.

Deno

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

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

Aset

Bget

Cdelete

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

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

Trying to use 'update' which is not a KV method.

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

3fill in blank

hard

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

Deno

const result = await kv.[1](['user', '123']);
console.log(result.value);

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

Aset

Bget

Cfetch

Dretrieve

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using non-existent methods like 'fetch' or 'retrieve'.

The get method retrieves the value for the given key from the KV store.

4fill in blank

hard

Fill both blanks to delete a key and check if deletion was successful.

Deno

const deleteResult = await kv.[1](['session', 'abc']);
if (deleteResult.[2]) {
  console.log('Deleted successfully');
}

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

Adelete

Bsuccess

Cvalue

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' instead of 'delete' causes errors.

Checking 'value' instead of 'success' to confirm deletion.

The delete method removes a key. The success property shows if it worked.

5fill in blank

hard

Fill all three blanks to create a transaction that sets and deletes keys atomically.

Deno

const txn = kv.[1]();
txn.[2](['cart', 'item1'], { quantity: 2 });
txn.[3](['cart', 'item2']);
await txn.commit();

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

Aatomic

Bset

Cdelete

Dtransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'transaction' instead of 'atomic' to start.

Mixing up 'set' and 'delete' method calls inside the transaction.

Use atomic() to start a transaction, then set and delete to modify keys before committing.

Practice

1. What is the correct way to store a value in Deno KV?

easy

A. Use kv.set(["key"], value) to save data.

B. Use kv.save("key", value) to save data.

C. Use kv.put("key", value) to save data.

D. Use kv.store(["key"], value) to save data.

Solution

1. Step 1: Understand Deno KV key format

   Deno KV uses arrays as keys, so keys must be passed as arrays like ["key"].

2. Step 2: Identify the correct method to save data

   The method to save data is set, so kv.set(["key"], value) is correct.

3. Final Answer:

   Use kv.set(["key"], value) to save data. -> Option A

4. Quick Check:

   Key as array + set method = Use kv.set(["key"], value) to save data. [OK]

Hint: Remember: keys are arrays and method is set [OK]

Common Mistakes:

• Using string keys instead of array keys
• Using wrong method names like save or put
• Passing key as a single string instead of array

2. Which of the following is the correct syntax to read a value from Deno KV?

easy

A. const result = kv.get(["key"]);

B. const result = await kv.get("key");

C. const result = await kv.get(["key"]);

D. const result = kv.get("key");

Solution

1. Step 1: Recognize key format for get method

   Deno KV requires keys as arrays, so the key must be passed as ["key"].

2. Step 2: Confirm asynchronous usage of get

   The get method is asynchronous, so it must be awaited.

3. Final Answer:

   const result = await kv.get(["key"]); -> Option C

4. Quick Check:

   Await + array key + get method = const result = await kv.get(["key"]); [OK]

Hint: Always await get and use array keys [OK]

Common Mistakes:

• Not awaiting the get method
• Passing key as string instead of array
• Using synchronous call without await

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

const kv = await Deno.openKv();
await kv.set(["user", "name"], "Alice");
const result = await kv.get(["user", "name"]);
console.log(result.value);

medium

A. undefined

B. "Alice"

C. null

D. Throws an error

Solution

1. Step 1: Store value with key ["user", "name"]

   The code stores the string "Alice" under the key array ["user", "name"].

2. Step 2: Retrieve the stored value using the same key

   The get method fetches the stored value, which is "Alice".

3. Final Answer:

   "Alice" -> Option B

4. Quick Check:

   Set then get with same key returns stored value [OK]

Hint: Set then get with same key returns stored value [OK]

Common Mistakes:

• Expecting key as string instead of array
• Not awaiting async calls
• Confusing result object with direct value

4. Identify the error in this Deno KV usage:

const kv = await Deno.openKv();
await kv.set("session", "active");
const status = await kv.get(["session"]);
console.log(status.value);

medium

A. The key in set should be an array, not a string.

B. The get method should not be awaited.

C. The value "active" must be an object, not a string.

D. The console.log should print status directly, not status.value.

Solution

1. Step 1: Check key format in set method

   The set method requires the key to be an array, but here it is a string "session".

2. Step 2: Confirm correct key format for get method

   The get method uses the key as an array ["session"], which is correct.

3. Final Answer:

   The key in set should be an array, not a string. -> Option A

4. Quick Check:

   Key must be array in set and get [OK]

Hint: Keys must always be arrays in set and get [OK]

Common Mistakes:

• Using string keys instead of array keys
• Not awaiting async methods
• Misunderstanding value access from get result

5. You want to store user preferences with keys like ["user", userId, "prefs"] and values as objects. Which code correctly updates preferences for userId 42 without overwriting other keys?

const kv = await Deno.openKv();
const userId = 42;
const newPrefs = { theme: "dark" };
// Which code below is correct?

hard

A. await kv.set([userId, "prefs"], newPrefs);

B. await kv.set(["user", "prefs"], newPrefs);

C. await kv.set(["user", userId], newPrefs);

D. await kv.set(["user", userId, "prefs"], newPrefs);

Solution

1. Step 1: Understand key structure for user preferences

   The key must include "user", the userId, and "prefs" to uniquely identify preferences per user.

2. Step 2: Check which option uses the full key correctly

   await kv.set(["user", userId, "prefs"], newPrefs); uses ["user", userId, "prefs"] which matches the required key structure.

3. Final Answer:

   await kv.set(["user", userId, "prefs"], newPrefs); -> Option D

4. Quick Check:

   Full key array with userId keeps keys unique [OK]

Hint: Include userId in key array to avoid overwriting [OK]

Common Mistakes:

• Omitting userId from key causing overwrites
• Using incomplete key arrays
• Confusing order of key elements