What is Deno - Quick Revision & Key Takeaways

Recall & Review

beginner

What is Deno?

Deno is a modern runtime for JavaScript and TypeScript. It lets you run code outside the browser, like Node.js, but with better security and built-in tools.

intermediate

How does Deno improve security compared to Node.js?

Deno runs code in a secure sandbox by default. It blocks file, network, and environment access unless you explicitly allow it with flags.

beginner

Which languages does Deno support natively?

Deno supports JavaScript and TypeScript out of the box, so you can run both without extra setup.

intermediate

Name one built-in tool that comes with Deno.

Deno includes a built-in code formatter, a test runner, and a bundler, so you don't need extra tools for these tasks.

intermediate

Why was Deno created?

Deno was created by the same person who made Node.js to fix some design problems and add modern features like security and TypeScript support.

What is the main purpose of Deno?

A Design websites

B Create mobile apps

C Run JavaScript and TypeScript outside the browser

D Manage databases

Deno is a runtime to run JavaScript and TypeScript code outside the browser environment.

Which language does Deno support without extra setup?

A Python

B C++

C Ruby

D JavaScript

Deno supports JavaScript and TypeScript natively.

How does Deno handle security by default?

A Blocks all access unless allowed

B Requires a password

C Allows all access

D Runs code in the browser

Deno runs code in a secure sandbox and blocks file, network, and environment access unless explicitly allowed.

Who created Deno?

A Brendan Eich

B Ryan Dahl

C Guido van Rossum

D Linus Torvalds

Ryan Dahl created Deno as a modern alternative to Node.js.

Which of these is a built-in tool in Deno?

A Code formatter

B Database manager

C Image editor

D Web browser

Deno includes a built-in code formatter among other tools.

Explain what Deno is and why it was created.

Think about what problems Deno solves compared to Node.js.

Describe how Deno handles security differently from other runtimes.

Focus on what happens when you run code without special permissions.

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