Deno vs Node.js comparison - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import a module in Deno.

Deno

import { serve } from "https://deno.land/std/http/server.ts"; const server = serve({ port: [1] });

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

A80

B3000

C8080

D5000

Attempts:

3 left

💡 Hint

Common Mistakes

Using ports like 3000 which are common in Node.js but not shown here.

Leaving the port number blank or using invalid ports.

In Deno, you import modules directly from URLs. The port 8080 is commonly used for local servers.

2fill in blank

medium

Complete the code to read a file asynchronously in Deno.

Deno

const data = await Deno.[1]("./file.txt");

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

AreadFile

BwriteTextFile

CreadFileSync

DreadTextFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using readFileSync which is synchronous.

Using writeTextFile which writes instead of reads.

Deno provides readTextFile to read text files asynchronously and return a string.

3fill in blank

hard

Fix the error in the Deno permission request code.

Deno

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

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

Aquery

Brequest

Crevoke

Dcheck

Attempts:

3 left

💡 Hint

Common Mistakes

Using query which only checks permission status.

Using revoke which removes permission.

To ask the user for permission in Deno, use the request method.

4fill in blank

hard

Fill both blanks to create a simple HTTP server in Deno that responds with 'Hello World'.

Deno

import { serve } from "https://deno.land/std/http/server.ts";
for await (const req of serve({ port: [1] })) {
  req.[2](new Response("Hello World"));
}

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

A8080

BlistenAndServe

Crespond

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using listenAndServe which is not part of this import.

Using request instead of respond to send data.

The server listens on port 8080 and uses the respond method to send the response.

5fill in blank

hard

Fill all three blanks to create a Deno script that imports a local module and logs its default export.

Deno

import myFunc from "./mod.ts";
const result = myFunc([1]);
console.[2](result);
// Run with: deno run --allow-[3] script.ts

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

A"test input"

Blog

Cread

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string argument.

Using console.print or console.write which do not exist.

Using --allow-write instead of --allow-read.

The function is called with a string argument, the result is logged with console.log, and the script needs read permission to import local files.

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