KV on Deno Deploy - Mini Project: Build & Apply

Simple Key-Value Storage with KV on Deno Deploy

📖 Scenario: You are building a small web service on Deno Deploy that stores and retrieves user notes using the KV (Key-Value) storage system.This service will let users save a note with a unique key and then fetch it later.

🎯 Goal: Create a Deno Deploy script that uses KV to store a note under a key and then retrieve it.You will set up the KV store, define a key and a note, save the note, and then read it back.

📋 What You'll Learn

Create a KV store instance

Define a key and a note string

Store the note in KV using the key

Retrieve the note from KV using the key

💡 Why This Matters

🌍 Real World

Many web apps need to save small pieces of data quickly and retrieve them later. KV storage on Deno Deploy is perfect for simple note-taking apps, user preferences, or session data.

💼 Career

Understanding KV storage and serverless functions is important for backend and full-stack developers working with modern cloud platforms like Deno Deploy.

1

Set up KV store and define data

Create a constant called kv that gets the KV store from Deno.openKv(). Then create a constant noteKey with the value ["note", "1"] and a constant noteValue with the string "Remember to drink water".

Deno

# Your code here

Hint

Use await Deno.openKv() to get the KV store. Define the key as an array with two strings. The note is a simple string.

2

Store the note in KV

Use await kv.set(noteKey, noteValue) to save the note string under the key in the KV store.

Deno

const kv = await Deno.openKv();
const noteKey = ["note", "1"];
const noteValue = "Remember to drink water";

// Your code here

Hint

Use the set method on kv with the key and value to store data.

3

Retrieve the note from KV

Create a constant called result and assign it the value of await kv.get(noteKey) to fetch the stored note.

Deno

const kv = await Deno.openKv();
const noteKey = ["note", "1"];
const noteValue = "Remember to drink water";

await kv.set(noteKey, noteValue);

// Your code here

Hint

Use the get method on kv with the key to retrieve the stored value.

4

Access and export the stored note

Create a constant called storedNote and assign it the value property of result. Then export a default async function called handler that returns a new Response with storedNote as the body and content type text/plain.

Deno

const kv = await Deno.openKv();
const noteKey = ["note", "1"];
const noteValue = "Remember to drink water";

await kv.set(noteKey, noteValue);

const result = await kv.get(noteKey);

// Your code here

Hint

Extract the value from result. Then create an async function named handler that returns a plain text response with the stored note.

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