Business IT Support Cape Town

Core Modules

File System (fs)

fs.readFile(path, callback)

fs.readFileSync(path)

fs.writeFile(path, data, callback)

fs.writeFileSync(path, data)

fs.appendFile(path, data, callback)

fs.unlink(path, callback)

fs.mkdir(path, callback)

fs.rmdir(path, callback)

fs.readdir(path, callback)

fs.stat(path, callback)

fs.exists(path, callback)

fs.createReadStream(path)

fs.createWriteStream(path)

const fs = require('fs');

// Async file operations
fs.readFile('file.txt', 'utf8', (err, data) => {
    if (err) throw err;
    console.log(data);
});

// Sync file operations
const data = fs.readFileSync('file.txt', 'utf8');

// Promises (fs.promises)
const fsPromises = require('fs').promises;
async function readFile() {
    try {
        const data = await fsPromises.readFile('file.txt', 'utf8');
        return data;
    } catch (error) {
        console.error(error);
    }
}

HTTP Module

HTTP Server & Client

const http = require('http');

// Create HTTP server
const server = http.createServer((req, res) => {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end('Hello World!');
});

server.listen(3000, () => {
    console.log('Server running on port 3000');
});

// HTTP client request
const options = {
    hostname: 'www.example.com',
    port: 80,
    path: '/api/data',
    method: 'GET'
};

const req = http.request(options, (res) => {
    let data = '';
    res.on('data', (chunk) => {
        data += chunk;
    });
    res.on('end', () => {
        console.log(data);
    });
});

req.end();

Path Module

Path Operations

path.join(...paths)

path.resolve(...paths)

path.dirname(path)

path.basename(path)

path.extname(path)

path.parse(path)

path.format(pathObject)

path.isAbsolute(path)

path.relative(from, to)

path.normalize(path)

const path = require('path');

// Join paths
const fullPath = path.join('/users', 'john', 'documents', 'file.txt');

// Get directory name
const dir = path.dirname('/users/john/file.txt'); // '/users/john'

// Get file name
const file = path.basename('/users/john/file.txt'); // 'file.txt'

// Get extension
const ext = path.extname('/users/john/file.txt'); // '.txt'

Process & Global Objects

Process Object

process.argv

process.env

process.cwd()

process.exit(code)

process.pid

process.platform

process.version

process.uptime()

process.memoryUsage()

process.nextTick(callback)

// Command line arguments
console.log(process.argv);

// Environment variables
console.log(process.env.NODE_ENV);

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

// Exit process
process.exit(0);

// Process events
process.on('exit', (code) => {
    console.log(`Process exited with code ${code}`);
});

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

Events & Streams

EventEmitter

const EventEmitter = require('events');

class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();

// Add listener
myEmitter.on('event', (data) => {
    console.log('Event received:', data);
});

// Emit event
myEmitter.emit('event', 'Hello World');

// Once listener (fires only once)
myEmitter.once('start', () => {
    console.log('Started');
});

// Remove listener
const listener = () => console.log('Listener');
myEmitter.on('test', listener);
myEmitter.removeListener('test', listener);

Streams

const fs = require('fs');

// Readable stream
const readStream = fs.createReadStream('input.txt');
readStream.on('data', (chunk) => {
    console.log('Received chunk:', chunk);
});

// Writable stream
const writeStream = fs.createWriteStream('output.txt');
writeStream.write('Hello ');
writeStream.write('World!');
writeStream.end();

// Pipe streams
readStream.pipe(writeStream);

// Transform stream
const { Transform } = require('stream');
const upperCaseTransform = new Transform({
    transform(chunk, encoding, callback) {
        this.push(chunk.toString().toUpperCase());
        callback();
    }
});

readStream.pipe(upperCaseTransform).pipe(writeStream);

Utilities & Modules

URL Module

const url = require('url');

// Parse URL
const myURL = new URL('https://example.com:8000/path?query=value#hash');
console.log(myURL.hostname); // 'example.com'
console.log(myURL.pathname); // '/path'
console.log(myURL.search);   // '?query=value'

// Legacy URL parsing
const parsed = url.parse('https://example.com/path?query=value');
console.log(parsed.host);     // 'example.com'
console.log(parsed.pathname); // '/path'

Crypto Module

const crypto = require('crypto');

// Generate hash
const hash = crypto.createHash('sha256');
hash.update('Hello World');
console.log(hash.digest('hex'));

// Generate random bytes
crypto.randomBytes(16, (err, buffer) => {
    if (err) throw err;
    console.log(buffer.toString('hex'));
});

// HMAC
const hmac = crypto.createHmac('sha256', 'secret-key');
hmac.update('data to hash');
console.log(hmac.digest('hex'));

OS Module

os.platform()

os.arch()

os.cpus()

os.totalmem()

os.freemem()

os.hostname()

os.uptime()

os.userInfo()

os.homedir()

os.tmpdir()

NPM & Package Management

Package.json

{
  "name": "my-app",
  "version": "1.0.0",
  "description": "My Node.js application",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "dev": "nodemon index.js",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.18.0",
    "lodash": "^4.17.21"
  },
  "devDependencies": {
    "nodemon": "^2.0.15",
    "jest": "^27.5.1"
  },
  "engines": {
    "node": ">=14.0.0"
  }
}

NPM Commands

npm init

npm install package

npm install -g package

npm install --save-dev package

npm uninstall package

npm update

npm list

npm run script

npm publish

npm version patch/minor/major

Outsourced IT Partner

🟢 Node.js Runtime Environment