What is Deno - Performance Impact

Performance: What is Deno

MEDIUM IMPACT

Deno affects the server-side runtime performance and startup speed of JavaScript and TypeScript applications.

Running JavaScript/TypeScript code efficiently on the server

Deno

deno run app.ts

Deno runs TypeScript natively and has faster startup with built-in security and modern V8 optimizations.

📈 Performance Gainreduces startup time by 30-50ms and lowers memory overhead

Running JavaScript/TypeScript code efficiently on the server

Deno

node app.js

Node.js requires separate tools for TypeScript and has a larger startup time due to legacy design.

📉 Performance Costblocks startup for 100-200ms depending on app size

Performance Comparison

Pattern	Startup Time	Memory Usage	Module Loading	Verdict
Node.js with separate TypeScript compiler	100-200ms	Higher	Slower due to transpilation	[X] Bad
Deno native TypeScript runtime	50-100ms	Lower	Faster with caching	[OK] Good

Rendering Pipeline

Deno does not affect browser rendering but impacts server-side runtime performance and response speed.

→Script Parsing

→Execution

→Module Loading

⚠️ BottleneckModule Loading and Script Parsing

Optimization Tips

1Use Deno's native TypeScript support to reduce startup time.

2Leverage Deno's caching to speed up module loading.

3Enable permissions only as needed to maintain security without slowing runtime.

Performance Quiz - 3 Questions

What is a key performance advantage of Deno over Node.js?

A Native TypeScript support reducing startup time

B Uses older JavaScript engines for compatibility

C Requires separate tools for TypeScript compilation

D Has slower module loading due to legacy design

DevTools: Performance

How to check: Run your Deno application with --inspect flag, open Chrome DevTools Performance panel, and record startup and execution times.

What to look for: Look for script parsing and module loading durations to confirm faster startup and execution.

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