What is Deno - Hands-On Activity

What is Deno

📖 Scenario: You are curious about modern tools for running JavaScript and TypeScript outside the browser. You want to learn about Deno, a new runtime that helps run code safely and simply.

🎯 Goal: Understand what Deno is and create a simple Deno script that prints a greeting message.

📋 What You'll Learn

Create a variable called message with the value 'Hello from Deno!'

Write a line that outputs message using console.log

💡 Why This Matters

🌍 Real World

Deno is used to build server-side applications, scripts, and tools that run JavaScript or TypeScript safely and efficiently.

💼 Career

Knowing Deno helps you work with modern JavaScript runtimes, useful for backend development and scripting in many tech jobs.

1

Create a message variable

Create a variable called message and set it to the string 'Hello from Deno!'.

Deno

# Your code here

Hint

Use const to create a variable that does not change.

2

Print the message

Use console.log to print the variable message to the console.

Deno

const message = 'Hello from Deno!';
# Your code here

Hint

console.log shows text in the terminal where you run your Deno script.

3

Add a comment about Deno

Add a comment at the top of the file that says // Deno is a secure runtime for JavaScript and TypeScript.

Deno

# Your code here
const message = 'Hello from Deno!';
console.log(message);

Hint

Comments start with // and explain the code without running.

4

Run your Deno script

Save your code in a file called hello.ts and run it using the command deno run hello.ts in your terminal.

Deno

// Your code is ready to run with Deno
// Run: deno run hello.ts

Hint

Use your terminal to run the script and see the message printed.

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