Deno KV (built-in key-value store) - Step-by-Step Execution

Concept Flow - Deno KV (built-in key-value store)

Start Deno KV Client

↓

Open or Create KV Store

↓

Perform Operation: Get/Set/Delete

↓

Check Operation Result

↓

Use Result or Handle Error

↓

Close or Continue with KV Store

This flow shows how Deno KV client starts, opens the store, performs operations like get/set/delete, checks results, and then continues or closes.

Execution Sample

Deno

import { openKv } from "deno:kv";

const kv = await openKv();
await kv.set(["user", "123"], { name: "Alice" });
const user = await kv.get(["user", "123"]);
console.log(user?.value);

This code opens the KV store, sets a user object with key ["user", "123"], then gets and logs the stored user.

Execution Table

Step	Action	Key	Value	Result	Notes
1	openKv()	-	-	kv client object	KV store client is ready
2	set()	["user", "123"]	{"name":"Alice"}	void	Value stored under key
3	get()	["user", "123"]	-	{"value":{"name":"Alice"}}	Value retrieved successfully
4	console.log()	-	-	Alice	Output user name to console
5	-	-	-	-	End of operations

💡 All operations completed successfully, KV store interaction finished.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
kv	undefined	kv client object	kv client object	kv client object	kv client object
user	undefined	undefined	undefined	{"value":{"name":"Alice"}}	{"value":{"name":"Alice"}}

Key Moments - 2 Insights

Why do we use an array like ["user", "123"] as the key instead of a simple string?

Deno KV uses arrays as keys to allow hierarchical or composite keys, making it easier to organize and query data. See Step 2 and 3 in execution_table where the key is an array.

What does the get() method return if the key does not exist?

The get() method returns null or an object with value null if the key is missing. This is important to check before using the value. In the execution_table, Step 3 shows a successful get with a value.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'user' after Step 3?

A {"value":{"name":"Alice"}}

B undefined

C null

D {"name":"Alice"}

💡 Hint

Check the 'Result' column in Step 3 of execution_table.

At which step is the value stored in the KV store?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for the 'set()' action in the execution_table.

If we change the key to ["user", "124"], what will happen at Step 3?

A set() fails

B get() returns the same user Alice

C get() returns null or no value

D openKv() fails

💡 Hint

Refer to key usage in Steps 2 and 3; different keys store different values.

Concept Snapshot

Deno KV is a built-in key-value store.
Use openKv() to get a client.
Keys are arrays for structured data.
Use set(key, value) to store.
Use get(key) to retrieve.
Check get() result before use.

Full Transcript

This visual execution shows how to use Deno KV, a built-in key-value store. First, open the KV client with openKv(). Then, store data using set() with a key array like ["user", "123"] and a value object. Next, retrieve the data with get() using the same key. The get() returns an object containing the stored value or null if missing. Finally, use the retrieved value as needed, such as logging it. Keys as arrays help organize data hierarchically. Always check get() results before using them to avoid errors.

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