Why Deno is secure by default - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run a Deno script with permission to read files.

Deno

deno run [1] script.ts

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

A--allow-net

B--allow-write

C--allow-read

D--allow-env

Attempts:

3 left

💡 Hint

Common Mistakes

Using network permission flag instead of read permission.

The --allow-read flag grants permission to read files, which Deno blocks by default for security.

2fill in blank

medium

Complete the code to allow a Deno script to access environment variables.

Deno

deno run [1] script.ts

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

A--allow-env

B--allow-net

C--allow-read

D--allow-run

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing environment access with file read permission.

The --allow-env flag lets the script access environment variables, which is blocked by default.

3fill in blank

hard

Fix the error in the command to allow network access in Deno.

Deno

deno run [1] script.ts

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

A--network

B--allow-network

C--net-allow

D--allow-net

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect flag names like '--allow-network' or '--net-allow'.

The correct flag for network access is --allow-net. Other options are invalid and cause errors.

4fill in blank

hard

Fill both blanks to run a Deno script with permissions to read files and run subprocesses.

Deno

deno run [1] [2] script.ts

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

A--allow-read

B--allow-net

C--allow-run

D--allow-env

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing network permission with run permission.

--allow-read grants file read access, and --allow-run allows running subprocesses. Both are needed here.

5fill in blank

hard

Fill all three blanks to run a Deno script with permissions to read files, access environment variables, and use the network.

Deno

deno run [1] [2] [3] script.ts

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

A--allow-write

B--allow-env

C--allow-net

D--allow-read

Attempts:

3 left

💡 Hint

Common Mistakes

Including write permission when not needed.

The flags --allow-read, --allow-env, and --allow-net grant permissions for file reading, environment access, and network use respectively.

Practice

1. Why does Deno block file and network access by default?

easy

A. To protect your computer from harmful or unknown code

B. Because it does not support file or network operations

C. To make programs run faster

D. Because it only runs in offline mode

Solution

1. Step 1: Understand Deno's security design

   Deno is designed to be secure by default to protect users from running unsafe code.

2. Step 2: Reason about default blocking

   Blocking file and network access prevents malicious code from harming your system without permission.

3. Final Answer:

   To protect your computer from harmful or unknown code -> Option A

4. Quick Check:

   Security by default = Protect computer [OK]

Hint: Deno blocks risky actions to keep your system safe [OK]

Common Mistakes:

• Thinking Deno lacks file/network features
• Assuming blocking improves speed
• Believing Deno runs only offline

2. Which command correctly runs a Deno script with permission to read files?

easy

A. deno run --allow-file script.ts

B. deno run --allow-read script.ts

C. deno run --read script.ts

D. deno run --file-access script.ts

Solution

1. Step 1: Recall Deno permission flags

   Deno uses flags like --allow-read to grant file read access explicitly.

2. Step 2: Identify correct syntax

   Only --allow-read is the valid flag to allow reading files in Deno.

3. Final Answer:

   deno run --allow-read script.ts -> Option B

4. Quick Check:

   File read permission flag = --allow-read [OK]

Hint: Use --allow-read to permit file reading in Deno [OK]

Common Mistakes:

• Using incorrect flags like --read or --allow-file
• Forgetting to add permission flags
• Confusing permission flag names

3. What will happen if you run this Deno script without any permission flags?

console.log(Deno.readTextFileSync("data.txt"));

medium

A. It prints the contents of data.txt

B. It runs without any output

C. It creates data.txt if missing

D. It throws a permission error

Solution

1. Step 1: Understand default permissions

   Deno blocks file reading unless --allow-read is given.

2. Step 2: Predict script behavior without permissions

   Trying to read a file without permission causes a runtime permission error.

3. Final Answer:

   It throws a permission error -> Option D

4. Quick Check:

   No permission = permission error [OK]

Hint: No --allow-read means file read causes error [OK]

Common Mistakes:

• Assuming file reads succeed without permission
• Thinking file is created automatically
• Expecting silent failure without error

4. You run this command but get a permission error:
deno run script.ts
How do you fix it to allow network access?

medium

A. No fix needed, network is allowed by default

B. Add --allow-network flag to the command

C. Add --allow-net flag to the command

D. Add --net-access flag to the command

Solution

1. Step 1: Identify correct network permission flag

   Deno requires --allow-net to permit network access explicitly.

2. Step 2: Correct the command

   Adding --allow-net fixes the permission error for network operations.

3. Final Answer:

   Add --allow-net flag to the command -> Option C

4. Quick Check:

   Network permission flag = --allow-net [OK]

Hint: Use --allow-net to enable network access in Deno [OK]

Common Mistakes:

• Using wrong flag like --allow-network or --net-access
• Assuming network is allowed by default
• Not adding any permission flag

5. You want to run a Deno script that reads a file and makes a network request. Which command grants the minimum permissions needed?

hard

A. deno run --allow-read --allow-net script.ts

B. deno run --allow-all script.ts

C. deno run --allow-write --allow-net script.ts

D. deno run --allow-read script.ts

Solution

1. Step 1: Identify required permissions

   Reading a file needs --allow-read; network requests need --allow-net.

2. Step 2: Choose minimal permissions

   --allow-read and --allow-net together grant only needed access, no extras.

3. Step 3: Eliminate incorrect options

   --allow-all grants too much; --allow-write is unnecessary; --allow-read alone misses network.

4. Final Answer:

   deno run --allow-read --allow-net script.ts -> Option A

5. Quick Check:

   Minimal needed permissions = --allow-read + --allow-net [OK]

Hint: Grant only needed permissions: read + net for this script [OK]

Common Mistakes:

• Using --allow-all when minimal is better
• Confusing --allow-write with --allow-read
• Forgetting network permission