Permission prompts at runtime in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to request read permission at runtime.

Deno

const status = await Deno.permissions.[1]({ name: "read" });

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

Arequest

Bquery

Crevoke

Dcheck

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'query' instead of 'request' which only checks permission without prompting.

Using 'revoke' which removes permission instead of requesting it.

The request method asks the user for permission at runtime.

2fill in blank

medium

Complete the code to check if write permission is already granted.

Deno

const status = await Deno.permissions.[1]({ name: "write" });
if (status.state === "granted") {
  console.log("Write permission granted.");
}

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

Aquery

Bcheck

Crevoke

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' which prompts the user unnecessarily.

Using 'revoke' which removes permission.

The query method checks the current permission state without prompting the user.

3fill in blank

hard

Fix the error in the code to revoke net permission.

Deno

await Deno.permissions.[1]({ name: "net" });

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

Arequest

Brevoke

Cquery

Dcheck

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' which asks for permission instead of revoking it.

Using 'query' which only checks permission.

The revoke method removes previously granted permission.

4fill in blank

hard

Fill both blanks to request permission and check if it was granted.

Deno

const status = await Deno.permissions.[1]({ name: "[2]" });
if (status.state === "granted") {
  console.log("Permission granted.");
}

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

Arequest

Bquery

Cread

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'query' instead of 'request' for asking permission.

Using wrong permission names like 'execute'.

Use request to ask for permission and specify the permission name like read.

5fill in blank

hard

Fill all three blanks to check, request, and revoke run permission.

Deno

const status = await Deno.permissions.[1]({ name: "run" });
if (status.state !== "granted") {
  await Deno.permissions.[2]({ name: "run" });
}
await Deno.permissions.[3]({ name: "run" });

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

Aquery

Brequest

Crevoke

Dcheck

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'query' and 'request' methods.

Using 'check' which is not a Deno permissions method.

First, query checks permission, then request asks for it, and finally revoke removes it.

Practice

1. What does Deno.permissions.query() do in a Deno program?

easy

A. It checks if a specific permission is already granted or denied.

B. It automatically grants all permissions to the program.

C. It revokes permissions from the program at runtime.

D. It lists all permissions the program will request in the future.

Solution

1. Step 1: Understand the purpose of Deno.permissions.query()

   This method is used to check the current status of a permission, whether it is granted, denied, or prompt.

2. Step 2: Compare with other permission methods

   Unlike request() which asks for permission, query() only checks the status without changing it.

3. Final Answer:

   It checks if a specific permission is already granted or denied. -> Option A

4. Quick Check:

   Permission check = A [OK]

Hint: Query checks status without changing permissions [OK]

Common Mistakes:

• Confusing query() with request()
• Thinking query() grants permissions
• Assuming query() revokes permissions

2. Which of the following is the correct syntax to request read permission for the file data.txt in Deno?

easy

A. await Deno.permissions.request("read", "data.txt");

B. Deno.permissions.request({ permission: "read", file: "data.txt" });

C. await Deno.permissions.request({ name: "read", path: "data.txt" });

D. Deno.permissions.query({ name: "read", path: "data.txt" });

Solution

1. Step 1: Identify correct method and parameters

   The request() method takes an object with a name property for permission type and optional path for file-specific permission.

2. Step 2: Check syntax correctness

   await Deno.permissions.request({ name: "read", path: "data.txt" }); uses correct async call with an object containing name: "read" and path: "data.txt". Other options misuse parameters or use query instead of request.

3. Final Answer:

   await Deno.permissions.request({ name: "read", path: "data.txt" }); -> Option C

4. Quick Check:

   Correct request syntax = B [OK]

Hint: Use object with name and path in request() [OK]

Common Mistakes:

• Passing parameters as separate arguments
• Using query() instead of request()
• Wrong property names like permission or file

3. Consider this code snippet in Deno:

const status = await Deno.permissions.query({ name: "net" });
console.log(status.state);

If the program has not requested network permission yet, what will be printed?

medium

A. "granted"

B. "denied"

C. An error is thrown

D. "prompt"

Solution

1. Step 1: Understand default permission state

   When a permission like "net" is queried before any request, Deno returns the state "prompt" indicating user has not yet granted or denied.

2. Step 2: Confirm no error thrown on query

   Querying permission does not throw errors; it returns the current state as a string.

3. Final Answer:

   "prompt" -> Option D

4. Quick Check:

   Unrequested permission state = prompt [OK]

Hint: Unasked permissions show 'prompt' state [OK]

Common Mistakes:

• Assuming default is granted or denied
• Expecting an error on query
• Confusing query() with request() behavior

4. What is wrong with this Deno code snippet?

const permission = Deno.permissions.request({ name: "read" });
if (permission.state === "granted") {
  console.log("Access allowed");
}

medium

A. Missing await before Deno.permissions.request call.

B. Using wrong permission name "read" instead of "readFile".

C. Cannot check permission.state directly; must use a callback.

D. request() does not return a permission status object.

Solution

1. Step 1: Check async usage of request()

   The request() method returns a Promise, so it must be awaited to get the permission status object.

2. Step 2: Identify missing await impact

   Without await, permission is a Promise, so accessing permission.state is invalid and causes errors.

3. Final Answer:

   Missing await before Deno.permissions.request call. -> Option A

4. Quick Check:

   Always await request() for permission object [OK]

Hint: Always await async permission requests [OK]

Common Mistakes:

• Forgetting await on async calls
• Confusing permission names
• Trying to use callbacks instead of promises

5. You want to write a Deno script that reads a file only if the user grants permission at runtime. Which approach correctly handles permission requests and reading the file?

hard

A. const status = Deno.permissions.query({ name: "read", path: "file.txt" });
if (status.state === "granted") {
const data = Deno.readTextFileSync("file.txt");
console.log(data);
}

B. const status = await Deno.permissions.request({ name: "read", path: "file.txt" });
if (status.state === "granted") {
const data = await Deno.readTextFile("file.txt");
console.log(data);
} else {
console.log("Permission denied.");
}

C. await Deno.readTextFile("file.txt");
console.log("File read without permission check.");

D. Deno.permissions.request({ name: "read" });
const data = await Deno.readTextFile("file.txt");
console.log(data);

Solution

1. Step 1: Request permission with await and check result

   const status = await Deno.permissions.request({ name: "read", path: "file.txt" }); if (status.state === "granted") { const data = await Deno.readTextFile("file.txt"); console.log(data); } else { console.log("Permission denied."); } correctly awaits the permission request and checks if the state is "granted" before proceeding.

2. Step 2: Read file only if permission granted

   It reads the file asynchronously only after permission is granted, otherwise it informs the user permission was denied.

3. Step 3: Identify errors in other options

   const status = Deno.permissions.query({ name: "read", path: "file.txt" }); if (status.state === "granted") { const data = Deno.readTextFileSync("file.txt"); console.log(data); } uses query() which does not request permission; await Deno.readTextFile("file.txt"); console.log("File read without permission check."); reads without permission check; Deno.permissions.request({ name: "read" }); const data = await Deno.readTextFile("file.txt"); console.log(data); does not await request() and reads file regardless.

4. Final Answer:

   const status = await Deno.permissions.request({ name: "read", path: "file.txt" }); if (status.state === "granted") { const data = await Deno.readTextFile("file.txt"); console.log(data); } else { console.log("Permission denied."); } -> Option B

5. Quick Check:

   Request permission, await result, then read file [OK]

Hint: Always await request() and check state before file access [OK]

Common Mistakes:

• Using query() instead of request() to ask permission
• Not awaiting async permission requests
• Reading files without permission check