JavaScript Code → Parser → Abstract Syntax Tree (AST) → Interpreter (Ignition)
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                                              Hot Code Optimization (TurboFan)
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                                                    Machine Code Execution

node -v
npm -v

$ node
> console.log("Hello from Node.js!");
Hello from Node.js!
undefined
> 1 + 1
2

const message = "Hello, World!";
console.log(message);

const add = (a, b) => a + b;
console.log("2 + 3 =", add(2, 3));

node app.js

Hello, World!
2 + 3 = 5

console.log(global);

// Common globals
console.log(__dirname); // Path to current directory
console.log(__filename); // Path to current file

   ┌───────────────────────────┐
┌─>│           timers          │ ← setTimeout, setInterval
│  └─────────────┬─────────────┘
│  ┌─────────────┴─────────────┐
│  │     pending callbacks     │ ← I/O callbacks deferred
│  └─────────────┬─────────────┘
│  ┌─────────────┴─────────────┐
│  │       idle, prepare       │ ← internal use only
│  └─────────────┬─────────────┘      ┌───────────────┐
│  ┌─────────────┴─────────────┐      │   incoming    │
│  │           poll            │<─────┤  connections, │
│  └─────────────┬─────────────┘      │   data, etc.  │
│  ┌─────────────┴─────────────┐      └───────────────┘
│  │           check           │ ← setImmediate
│  └─────────────┬─────────────┘
│  ┌─────────────┴─────────────┐
└──┤      close callbacks      │ ← socket.on('close')
   └───────────────────────────┘

// This example reveals the priority order of Node.js async mechanisms.
// Synchronous code ALWAYS runs first, then the microtask queues, then the event loop phases.

console.log('1: Start');  // Synchronous -- runs immediately

setTimeout(() => {
  console.log('2: Timeout callback');  // Timers phase -- queued in the event loop
}, 0);  // Even with 0ms delay, this waits for the next event loop iteration

setImmediate(() => {
  console.log('3: Immediate callback');  // Check phase -- runs after I/O polling
});

process.nextTick(() => {
  console.log('4: Next tick callback');  // Microtask -- runs BEFORE the event loop continues
});

Promise.resolve().then(() => {
  console.log('5: Promise resolved');  // Microtask -- runs after nextTick, before event loop
});

console.log('6: End');  // Synchronous -- runs immediately

// Output:
// 1: Start
// 6: End
// 4: Next tick callback   (nextTick queue drains first)
// 5: Promise resolved     (promise microtasks drain second)
// 2: Timeout callback     (timers phase -- order with setImmediate varies outside I/O)
// 3: Immediate callback   (check phase)

// Environment variables
console.log(process.env.NODE_ENV);  // 'development' or 'production'
console.log(process.env.PATH);       // System PATH

// Process info
console.log(process.pid);            // Process ID
console.log(process.ppid);           // Parent process ID
console.log(process.version);        // Node.js version
console.log(process.versions);       // All dependency versions
console.log(process.platform);       // 'darwin', 'win32', 'linux'
console.log(process.arch);           // 'x64', 'arm64', etc.

// Command line arguments
console.log(process.argv);           // Array of arguments
// node app.js --port=3000
// ['path/to/node', 'path/to/app.js', '--port=3000']

// Current working directory
console.log(process.cwd());

// Memory usage
console.log(process.memoryUsage());
// { rss: 30093312, heapTotal: 6537216, heapUsed: 4195024, external: 8272 }

// Handle uncaught exceptions
process.on('uncaughtException', (err) => {
  console.error('Uncaught Exception:', err);
  process.exit(1);
});

// Handle unhandled promise rejections
process.on('unhandledRejection', (reason, promise) => {
  console.error('Unhandled Rejection at:', promise, 'reason:', reason);
});

// Graceful shutdown
process.on('SIGTERM', () => {
  console.log('SIGTERM received. Shutting down gracefully...');
  server.close(() => {
    console.log('Process terminated');
    process.exit(0);
  });
});

// Before exit
process.on('beforeExit', (code) => {
  console.log('Process beforeExit event with code:', code);
});

# Install NVM
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash

# Install Node versions
nvm install 20      # Install Node 20
nvm install 18      # Install Node 18
nvm use 20          # Switch to Node 20
nvm alias default 20 # Set default version
nvm list            # List installed versions

# Download from https://github.com/coreybutler/nvm-windows
nvm install 20.0.0
nvm use 20.0.0

my-node-app/
├── src/
│   ├── config/         # Configuration files
│   ├── controllers/    # Route controllers
│   ├── middleware/     # Custom middleware
│   ├── models/         # Database models
│   ├── routes/         # Route definitions
│   ├── services/       # Business logic
│   ├── utils/          # Utility functions
│   └── app.js          # Express app setup
├── tests/              # Test files
├── .env                # Environment variables
├── .env.example        # Environment template
├── .gitignore
├── package.json
└── README.md