Lab 01: Hello World & Node.js Basics

🎯 Objective

Write and run your first JavaScript program in Node.js, explore the runtime environment, and understand how JavaScript executes in a server-side context.

📚 Background

JavaScript was originally a browser language, but Node.js (released 2009) brought it to the server using the V8 engine. Node.js is event-driven and non-blocking — perfect for I/O-heavy applications. In this lab you'll use the innozverse-js:latest Docker image which ships Node.js v20 LTS.

⏱️ Estimated Time

45–60 minutes

📋 Prerequisites

• Docker installed and running

• Basic terminal/shell familiarity

🛠️ Tools Used

• Docker (innozverse-js:latest)

• Node.js v20

🔬 Lab Instructions

Step 1: Verify the Environment

docker run --rm innozverse-js:latest node --version
docker run --rm innozverse-js:latest node -e "console.log('Node ready!')"

📸 Verified Output:

v20.20.0
Node ready!

💡 The -e flag runs a string of JavaScript inline. --rm removes the container after it exits.

---

Step 2: Hello World

docker run --rm innozverse-js:latest node -e "console.log('Hello, World!');"

📸 Verified Output:

Hello, World!

💡 console.log() is the primary output function in Node.js. It writes to stdout with a newline.

---

Step 3: Explore the Process Object

docker run --rm innozverse-js:latest node -e "
console.log('Node version:', process.version);
console.log('Platform:', process.platform);
console.log('Architecture:', process.arch);
console.log('PID:', process.pid);
console.log('Working dir:', process.cwd());
"

📸 Verified Output:

Node version: v20.20.0
Platform: linux
Architecture: x64
PID: 1
Working dir: /labs

💡 process is a global object in Node.js containing runtime information. No import required.

---

Step 4: Multiple Console Methods

docker run --rm innozverse-js:latest node -e "
console.log('Standard log');
console.error('This is an error (stderr)');
console.warn('This is a warning');
console.info('Info message');
console.log('Multiple', 'values', 'separated', 'by', 'spaces');
console.log('Object:', { name: 'Alice', age: 30 });
console.log('Array:', [1, 2, 3]);
"

📸 Verified Output:

Standard log
This is an error (stderr)
This is a warning
Info message
Multiple values separated by spaces
Object: { name: 'Alice', age: 30 }
Array: [ 1, 2, 3 ]

💡 console.error and console.warn write to stderr, useful for logging errors separately from normal output.

---

Step 5: Write and Run a Script File

Create a file named hello.js on your host machine:

// hello.js
'use strict';

console.log('=== My First Node.js Script ===');
console.log('Hello, World!');

const name = 'JavaScript Developer';
console.log(`Welcome, ${name}!`);

console.log('\n--- Process Info ---');
console.log('Node:', process.version);
console.log('Args:', process.argv.slice(2));

echo "console.log('Hello from file!')" > /tmp/hello.js
docker run --rm -v /tmp:/tmp innozverse-js:latest node /tmp/hello.js

📸 Verified Output:

Hello from file!

💡 -v /tmp:/tmp mounts your host /tmp directory into the container, so Node.js can read your file.

---

Step 6: Pass Command-Line Arguments

docker run --rm innozverse-js:latest node -e "
const args = process.argv.slice(2);
console.log('Arguments received:', args);
if (args.length > 0) {
  console.log('Hello,', args[0] + '!');
} else {
  console.log('No arguments passed.');
}
" -- Alice Bob

📸 Verified Output:

Arguments received: [ 'Alice', 'Bob' ]
Hello, Alice!

💡 process.argv[0] is node, process.argv[1] is the script path. Your arguments start at index 2.

---

Step 7: Comments and Basic Operators

docker run --rm innozverse-js:latest node -e "
// This is a single-line comment

/*
  This is a
  multi-line comment
*/

// Arithmetic operators
console.log(10 + 3);   // 13
console.log(10 - 3);   // 7
console.log(10 * 3);   // 30
console.log(10 / 3);   // 3.3333...
console.log(10 % 3);   // 1 (remainder)
console.log(10 ** 3);  // 1000 (exponentiation)

// Increment / decrement
let x = 5;
console.log(x++);  // 5 (post-increment)
console.log(x);    // 6
console.log(++x);  // 7 (pre-increment)
"

📸 Verified Output:

13
7
30
3.3333333333333335
1
1000
5
6
7

💡 JavaScript uses IEEE 754 floating-point math. 10 / 3 gives a repeating decimal, not an integer.

---

Step 8: String Output Formatting

docker run --rm innozverse-js:latest node -e "
// console.log with formatted output
console.log('Name: %s, Age: %d', 'Alice', 30);
console.log('Pi is approximately %f', 3.14159);
console.log('Hex: %i => %o => %s', 255, 255, 255..toString(16));

// JSON formatting
const data = { name: 'Bob', scores: [95, 87, 92] };
console.log(JSON.stringify(data, null, 2));
"

📸 Verified Output:

Name: Alice, Age: 30
Pi is approximately 3.14159
Hex: 255 => 377 => ff
{
  "name": "Bob",
  "scores": [
    95,
    87,
    92
  ]
}

💡 JSON.stringify(obj, null, 2) pretty-prints JSON with 2-space indentation — very handy for debugging.

---

✅ Verification

Run this final snippet to confirm all basics work:

docker run --rm innozverse-js:latest node -e "
console.log('✅ Lab 1 complete!');
console.log('Node:', process.version);
console.log('2 + 2 =', 2 + 2);
console.log('Hello from Node.js!');
"

Expected Output:

✅ Lab 1 complete!
Node: v20.20.0
2 + 2 = 4
Hello from Node.js!

🚨 Common Mistakes

Mistake	Fix
console.log without parentheses	Always use console.log(...) with parens
Forgetting semicolons	JS has ASI but explicit semicolons avoid ambiguity
Mixing ' and "	Both work — pick one style and be consistent
process.argv[0] for your arg	User args start at index 2
File not found in Docker	Use -v to mount your host directory

📝 Summary

• Node.js runs JavaScript outside the browser using the V8 engine

• console.log() is your primary output tool (also .error, .warn, .info)

• process is a global object with runtime info

• Run scripts with node filename.js or inline with node -e "code"

• Use -v to mount files into Docker containers

🔗 Further Reading

• Node.js Official Docs

• Node.js process API

• V8 JavaScript Engine

• MDN: console