What is Deno - Interactive Quiz & Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print 'Hello from Deno!' in the console.

Deno

console.[1]('Hello from Deno!');

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

Awrite

Bprint

Cecho

Dlog

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' or 'echo' which are not valid in Deno.

Forgetting the parentheses.

The console.log function prints messages to the console in Deno.

2fill in blank

medium

Complete the code to import the standard HTTP server module in Deno.

Deno

import { serve } from '[1]';

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

Ahttps://deno.land/x/express

Bhttps://nodejs.org/http

Chttps://deno.land/std/http/server.ts

Dhttps://cdn.jsdelivr.net/npm/http

Attempts:

3 left

💡 Hint

Common Mistakes

Using Node.js or Express URLs which don't work in Deno.

Using CDN URLs not related to Deno standard modules.

Deno uses URLs to import modules. The standard HTTP server is imported from https://deno.land/std/http/server.ts.

3fill in blank

hard

Fix the error in the code to run a simple HTTP server in Deno.

Deno

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

const server = serve({ port: [1] });

for await (const req of server) {
  req.respond({ body: 'Hello Deno!' });
}

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

A8080

B'8080'

Cport

D80

Attempts:

3 left

💡 Hint

Common Mistakes

Using port as a string with quotes.

Using an undefined variable 'port'.

The port number must be a number, not a string. So use 8080 without quotes.

4fill in blank

hard

Fill in the blank to create a Deno script that reads a file and prints its content.

Deno

const data = await Deno.[1]('hello.txt');
console.log(new TextDecoder().decode(data));

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

AwriteFile

BreadFile

CreadTextFile

DremoveFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using writeFile instead of readFile.

Using removeFile which deletes files.

Deno.readFile reads a file as bytes, and readTextFile reads as text. Here, readFile is correct because the code decodes bytes manually.

5fill in blank

hard

Fill all three blanks to create a Deno script that fetches JSON data from a URL and logs a property.

Deno

const response = await fetch('[1]');
const data = await response.[2]();
console.log(data.[3]);

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

Ahttps://api.example.com/data

Bjson

Cname

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text' instead of 'json' to parse response.

Logging a property that doesn't exist.

The fetch function gets data from the URL. The json() method parses the response as JSON. Then we log the name property from the data.

Practice

1. What is Deno primarily used for?

easy

A. Running JavaScript and TypeScript outside the browser

B. Creating mobile apps

C. Designing websites with HTML and CSS

D. Managing databases

Solution

1. Step 1: Understand Deno's purpose

   Deno is a runtime environment that allows running JavaScript and TypeScript code outside of web browsers.

2. Step 2: Compare options with Deno's use

   Options A, B, and D describe other technologies or tasks unrelated to Deno's main function.

3. Final Answer:

   Running JavaScript and TypeScript outside the browser -> Option A

4. Quick Check:

   Deno runs JS/TS outside browser = C [OK]

Hint: Deno runs JS/TS outside browser, not for apps or design [OK]

Common Mistakes:

• Confusing Deno with frontend frameworks
• Thinking Deno manages databases
• Assuming Deno is for mobile app development

2. Which command correctly runs a Deno script named app.ts?

easy

A. deno execute app.ts

B. deno start app.ts

C. node app.ts

D. deno run app.ts

Solution

1. Step 1: Recall Deno's run command

   Deno uses the command deno run to execute scripts.

2. Step 2: Check other options

   deno execute app.ts uses 'execute' which is invalid, deno start app.ts uses 'start' which is not a Deno command, node app.ts uses 'node' which is for Node.js.

3. Final Answer:

   deno run app.ts -> Option D

4. Quick Check:

   Run scripts with 'deno run' = D [OK]

Hint: Use 'deno run' to execute scripts, not 'execute' or 'start' [OK]

Common Mistakes:

• Using 'node' instead of 'deno run'
• Typing 'deno execute' instead of 'deno run'
• Trying 'deno start' which is invalid

3. What will happen if you run deno run --allow-net app.ts?

medium

A. The script runs with permission to access the network

B. The script runs without any permissions

C. The script will fail due to missing permissions

D. The script runs with permission to access the file system

Solution

1. Step 1: Understand the permission flag

   The flag --allow-net grants the script permission to access network resources.

2. Step 2: Analyze the command effect

   Since the flag is present, the script can use network features. Other permissions like file system access are not granted.

3. Final Answer:

   The script runs with permission to access the network -> Option A

4. Quick Check:

   --allow-net grants network access = A [OK]

Hint: Flags like --allow-net control permissions; here network is allowed [OK]

Common Mistakes:

• Assuming no permissions are given without --allow-all
• Confusing network permission with file system permission
• Thinking script fails without --allow-net

4. Identify the error in this command: deno run --allow-read app.ts when app.ts tries to access the network.

medium

A. No error, network access is allowed by default

B. Error because --allow-read does not allow network access

C. Error because --allow-read is an invalid flag

D. No error, script runs with all permissions

Solution

1. Step 1: Understand permission flags

   The flag --allow-read only allows file system read access, not network access.

2. Step 2: Analyze script behavior

   If app.ts tries to access the network without --allow-net, it will cause a permission error.

3. Final Answer:

   Error because --allow-read does not allow network access -> Option B

4. Quick Check:

   --allow-read ≠ network permission = B [OK]

Hint: Network needs --allow-net; --allow-read is only for files [OK]

Common Mistakes:

• Assuming --allow-read grants network access
• Thinking all permissions are granted by default
• Using invalid flags

5. You want to run a Deno script server.ts that reads files and accesses the network securely. Which command should you use?

hard

A. deno run server.ts

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

C. deno run --allow-net --allow-read server.ts

D. deno run --allow-write server.ts

Solution

1. Step 1: Identify required permissions

   The script needs to read files and access the network, so it requires --allow-read and --allow-net.

2. Step 2: Evaluate options for security

   deno run --allow-net --allow-read server.ts grants only needed permissions. deno run --allow-all server.ts grants all permissions, which is less secure. deno run server.ts grants none. deno run --allow-write server.ts grants write access, which is unnecessary.

3. Final Answer:

   deno run --allow-net --allow-read server.ts -> Option C

4. Quick Check:

   Grant only needed permissions for security = A [OK]

Hint: Grant only needed permissions, avoid --allow-all for safety [OK]

Common Mistakes:

• Using --allow-all which is less secure
• Forgetting to add --allow-net for network access
• Adding unnecessary permissions like --allow-write