KV on Deno Deploy

Introduction

KV on Deno Deploy lets you store and get small pieces of data quickly on the cloud. It helps your app remember things between visits.

You want to save user preferences like theme or language.

You need to count how many times a page was visited.

You want to store short session data without a database.

You want to cache API responses to speed up your app.

Syntax

Deno

const kv = await Deno.openKv();

// Save data
await kv.set(["key"], "value");

// Get data
const result = await kv.get(["key"]);
const value = result.value;

Use await because these operations are asynchronous.

Keys are arrays like ["key"] and values can be strings, numbers, or JSON objects.

Examples

Save and get a simple string value.

Deno

await kv.set(["username"], "alice");
const result = await kv.get(["username"]);
const user = result.value;

Store and retrieve a number.

Deno

await kv.set(["count"], 5);
const result = await kv.get(["count"]);
const count = result.value;

Save and get an object with multiple values.

Deno

await kv.set(["settings"], { theme: "dark", fontSize: 16 });
const result = await kv.get(["settings"]);
const settings = result.value;

Sample Program

This simple server counts how many times the /visit path is called. It saves the count in KV and shows it to the user.

Deno

import { serve } from "https://deno.land/std@0.201.0/http/server.ts";

const kv = await Deno.openKv();

serve(async (req) => {
  const url = new URL(req.url);
  if (url.pathname === "/visit") {
    // Get current count or 0
    const result = await kv.get(["visit_count"]);
    const count = (result.value as number) ?? 0;
    // Increase count
    await kv.set(["visit_count"], count + 1);
    const numVisits = count + 1;
    const timeStr = numVisits === 1 ? "time" : "times";
    return new Response(`This page was visited ${numVisits} ${timeStr}.`);
  }
  return new Response("Use /visit to count visits.", { status: 404 });
});

Important Notes

KV storage is fast but best for small data, not big files.

Data saved in KV stays until you delete it or overwrite it.

Always handle missing keys by providing default values.

Summary

KV on Deno Deploy stores small data pieces in the cloud.

Use kv.set to save and kv.get to read data.

Great for counters, preferences, and caching.

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