Deno vs Node.js comparison - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Key difference in module import style

Which statement best describes how Deno handles module imports compared to Node.js?

A Node.js supports importing modules only via URLs, whereas Deno uses local files exclusively.

B Deno requires a package.json file for all projects, but Node.js does not.

C Deno uses URL-based imports directly without a package manager, while Node.js relies on npm and local node_modules folders.

D Both Deno and Node.js use the same import style and package management system.

💡 Hint

Think about how each environment finds and loads external code.

Deno allows importing modules directly from URLs, eliminating the need for a package manager like npm. Node.js depends on npm and local node_modules folders to manage packages.

❓ component_behavior

intermediate

Permission system behavior

What happens when you run a Deno script that tries to read a file without granting read permission?

Deno

deno run script.ts
// script.ts tries to read a local file

A The script runs normally and reads the file without any prompt.

B Deno throws a runtime error denying file access due to missing read permission.

C The script automatically requests permission from the user during execution.

D Deno ignores permissions and allows all file operations by default.

💡 Hint

Consider Deno's security model compared to Node.js.

Deno enforces explicit permissions for file system access. Without the --allow-read flag, it throws a runtime error denying access.

📝 Syntax

advanced

Correct way to run a Deno script with network access

Which command correctly runs a Deno script named app.ts with permission to access the network?

A deno run --allow-net app.ts

B deno run --net app.ts

C deno run --allow-network app.ts

D deno run --network app.ts

💡 Hint

Check the exact permission flag syntax Deno requires.

Deno uses the flag --allow-net to grant network access when running scripts.

🔧 Debug

advanced

Identify the cause of a runtime error in Deno

Given this Deno script, why does it throw a permission error when run with deno run script.ts?

const data = await Deno.readTextFile('info.txt');
console.log(data);

Deno

const data = await Deno.readTextFile('info.txt');
console.log(data);

A The script uses an unsupported API for reading files in Deno.

B The file 'info.txt' does not exist in the directory.

C The await keyword cannot be used at the top level in Deno.

D The script lacks the --allow-read flag to permit file reading.

💡 Hint

Think about Deno's permission system and command flags.

Deno requires explicit permission flags like --allow-read to read files. Without it, a permission error occurs.

❓ state_output

expert

Output difference between Deno and Node.js for ES module import

Consider this ES module import code in Deno and Node.js environments:

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

serve(() => new Response("Hello"));

What is the expected behavior when running this code in Deno vs Node.js without additional setup?

Deno

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

serve(() => new Response("Hello"));

A Deno runs the code successfully serving HTTP; Node.js throws a syntax or module resolution error.

B Both Deno and Node.js run the code successfully without errors.

C Both environments throw errors due to missing package.json.

D Node.js runs the code successfully; Deno throws a network permission error.

💡 Hint

Think about how each environment handles URL imports and permissions.

Deno supports direct URL imports and runs this code with proper permissions. Node.js does not support URL imports natively and will throw errors unless additional tools or loaders are used.

Practice

1. Which of the following is a key security feature of Deno compared to Node.js?

easy

A. Node.js has built-in sandboxing for all scripts.

B. Deno allows all file and network access without restrictions.

C. Deno runs code with restricted permissions by default.

D. Node.js requires explicit permission flags for network access.

Solution

1. Step 1: Understand Deno's default security model

   Deno runs scripts with no file, network, or environment access unless explicitly allowed.

2. Step 2: Compare with Node.js default behavior

   Node.js allows full access by default without permission restrictions.

3. Final Answer:

   Deno runs code with restricted permissions by default. -> Option C

4. Quick Check:

   Deno security = restricted by default [OK]

Hint: Remember: Deno locks down access unless you say otherwise [OK]

Common Mistakes:

• Thinking Node.js restricts permissions by default
• Assuming Deno allows all access without flags
• Confusing Node.js and Deno security models

2. Which syntax correctly runs a Deno script with network access permission?

easy

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

B. node run --allow-net script.ts

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

D. node run script.ts --allow-net

Solution

1. Step 1: Recall Deno command structure

   Deno uses deno run followed by permission flags before the script name.

2. Step 2: Identify correct flag placement

   The flag --allow-net must come before the script file name.

3. Final Answer:

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

4. Quick Check:

   Deno run + flags before script [OK]

Hint: Flags come before script name in Deno commands [OK]

Common Mistakes:

• Placing flags after the script name
• Using Node.js commands for Deno
• Mixing up 'node' and 'deno' commands

3. What will the following Deno code output if run without any permission flags?

console.log("Reading file...");
const data = await Deno.readTextFile("example.txt");
console.log(data);

medium

A. PermissionDenied: read access to 'example.txt' is not allowed

B. Contents of example.txt printed

C. SyntaxError due to await outside async function

D. FileNotFoundError if example.txt does not exist

Solution

1. Step 1: Check permission requirements for file reading

   Deno requires explicit --allow-read permission to read files.

2. Step 2: Analyze code run without permissions

   Running without --allow-read causes a PermissionDenied error when reading a file.

3. Final Answer:

   PermissionDenied: read access to 'example.txt' is not allowed -> Option A

4. Quick Check:

   Deno file read needs permission [OK]

Hint: Deno blocks file reads without --allow-read flag [OK]

Common Mistakes:

• Assuming file reads work without permission
• Confusing syntax errors with permission errors
• Ignoring Deno's security model

4. Identify the error in this Node.js code snippet compared to Deno's approach:

import { serve } from "https://deno.land/std/http/server.ts";
serve(() => new Response("Hello"));

medium

A. Node.js needs the 'serve' function to be called with 'new'.

B. Node.js cannot import modules directly from URLs like Deno.

C. Node.js does not support async functions.

D. Node.js requires 'require' instead of 'import'.

Solution

1. Step 1: Understand module import differences

   Deno supports direct URL imports; Node.js does not support this natively.

2. Step 2: Identify Node.js module system

   Node.js uses local files or npm packages, not direct URL imports.

3. Final Answer:

   Node.js cannot import modules directly from URLs like Deno. -> Option B

4. Quick Check:

   Node.js import URL support = no [OK]

Hint: Node.js needs local or npm modules, not URL imports [OK]

Common Mistakes:

• Thinking Node.js supports URL imports
• Confusing import syntax with async support
• Assuming 'new' is needed for serve function

5. You want to build a secure web server that only allows network access and no file system access. Which setup best fits this requirement using Deno and Node.js?

hard

A. Use Node.js with node --allow-net server.js to restrict file access.

B. Use Node.js with node server.js and rely on default security.

C. Use Deno with deno run server.ts without flags to allow all access.

D. Use Deno with deno run --allow-net server.ts to restrict file access.

Solution

1. Step 1: Identify security needs

   The server should allow only network access, no file system access.

2. Step 2: Compare Deno and Node.js permission models

   Deno allows fine-grained permission control via flags; Node.js does not restrict by default.

3. Step 3: Choose correct command

   deno run --allow-net server.ts grants network access only, blocking file system access.

4. Final Answer:

   Use Deno with deno run --allow-net server.ts to restrict file access. -> Option D

5. Quick Check:

   Deno permission flags enable precise access control [OK]

Hint: Deno flags control access; Node.js lacks default restrictions [OK]

Common Mistakes:

• Assuming Node.js restricts access by default
• Using Deno without flags allows no permissions
• Thinking Node.js supports --allow-net flag