Deno vs Node.js comparison - Performance Comparison

Performance: Deno vs Node.js comparison

MEDIUM IMPACT

This comparison affects server-side JavaScript runtime performance, impacting startup time, memory usage, and module loading speed.

Choosing a runtime for fast server startup and efficient module loading

Deno

Deno script using ES modules with URL imports and built-in TypeScript support

Deno caches remote modules and uses modern ES module loading, reducing startup time and memory usage.

📈 Performance Gainstartup time reduced by 30-50%, lower memory usage due to no node_modules

Choosing a runtime for fast server startup and efficient module loading

Deno

Node.js script with many CommonJS modules and large node_modules folder

Node.js loads many dependencies from disk and resolves CommonJS modules slower, causing slower startup and higher memory use.

📉 Performance Costblocks startup for 100-300ms depending on modules, higher memory footprint

Performance Comparison

Pattern	Startup Time	Memory Usage	Module Loading	Verdict
Node.js with CommonJS and node_modules	Slower (100-300ms)	Higher (due to large dependency trees)	Slower (disk-heavy resolution)	[X] Bad
Deno with ES modules and URL imports	Faster (50-150ms)	Lower (no node_modules folder)	Faster (cached remote modules)	[OK] Good

Rendering Pipeline

Though server-side runtimes don't render UI, their module loading and script execution affect response time and throughput.

→Module Loading

→Script Execution

→Caching

⚠️ BottleneckModule Loading and Dependency Resolution

Optimization Tips

1Use Deno for faster startup with ES module caching.

2Node.js may have slower startup due to CommonJS and large node_modules.

3Efficient module caching reduces server response delays.

Performance Quiz - 3 Questions

Which runtime generally has faster startup time due to modern module loading?

A Deno

B Node.js

C Both are equal

D Depends on the OS only

DevTools: Performance (Node.js) / Deno built-in profiler

How to check: Run the runtime with profiling enabled, measure startup time and memory usage, compare module load times.

What to look for: Look for total startup duration, memory peaks, and module load times to identify bottlenecks.

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