Node.js Cheat Sheet

Here’s a Node.js cheat sheet with common commands and snippets to help you with various tasks:

Basic Setup

Initialize a New Project:
```
  npm init -y
```
Install a Package:
```
  npm install package_name
```
Install a Package Globally:
```
  npm install -g package_name
```
Uninstall a Package:
```
  npm uninstall package_name
```
Run a Script:
```
  npm run script_name
```

Basic Server with HTTP Module

Simple HTTP Server:

  const http = require('http');

  const server = http.createServer((req, res) => {
      res.statusCode = 200;
      res.setHeader('Content-Type', 'text/plain');
      res.end('Hello, world!\n');
  });

  server.listen(3000, () => {
      console.log('Server running at http://localhost:3000/');
  });

Express Framework

Install Express:
```
  npm install express
```

Basic Express Server:

  const express = require('express');
  const app = express();

  app.get('/', (req, res) => {
      res.send('Hello, world!');
  });

  app.listen(3000, () => {
      console.log('Server running at http://localhost:3000/');
  });

Parse JSON Request Body:
```
  app.use(express.json());
```

Route Parameters:

  app.get('/user/:id', (req, res) => {
      res.send(`User ID: ${req.params.id}`);
  });

Middleware Example:

  const logger = (req, res, next) => {
      console.log(`${req.method} ${req.url}`);
      next();
  };

  app.use(logger);

File System (fs) Module

Read a File:

  const fs = require('fs');

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

Write to a File:

  fs.writeFile('file.txt', 'Hello, world!', (err) => {
      if (err) throw err;
      console.log('File has been saved!');
  });

Append to a File:

  fs.appendFile('file.txt', 'More data\n', (err) => {
      if (err) throw err;
      console.log('Data was appended to file!');
  });

Environment Variables

Using Environment Variables (.env):

Install dotenv:
```
 npm install dotenv
```

Load Environment Variables:

 require('dotenv').config();
 const port = process.env.PORT || 3000;

.env file example:
```
 PORT=3000
```

Asynchronous Patterns

Promises:

  const asyncFunction = () => {
      return new Promise((resolve, reject) => {
          setTimeout(() => resolve('Done!'), 1000);
      });
  };

  asyncFunction().then(result => console.log(result)).catch(error => console.error(error));

Async/Await:

  const asyncFunction = async () => {
      try {
          const result = await asyncTask();
          console.log(result);
      } catch (error) {
          console.error(error);
      }
  };

  asyncFunction();

Working with APIs (HTTP Requests)

Using Axios:

Install Axios:
```
 npm install axios
```

Make a GET Request:

 const axios = require('axios');

 axios.get('https://api.example.com/data')
     .then(response => console.log(response.data))
     .catch(error => console.error(error));

Using Fetch (in Node 18+):

  const fetch = require('node-fetch');

  fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => console.log(data))
      .catch(error => console.error(error));

Modules

Exporting a Module:

  // in math.js
  const add = (a, b) => a + b;
  module.exports = { add };

Importing a Module:

  // in main.js
  const { add } = require('./math');
  console.log(add(2, 3));

Error Handling

Basic Error Handling:

  try {
      const result = riskyOperation();
      console.log(result);
  } catch (error) {
      console.error('Error:', error.message);
  }

Handle Promise Rejections:

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

Debugging

Run with Debugger:
```
  node --inspect-brk app.js
```

Using console.log() for Debugging:

  const variable = 'test';
  console.log({ variable });

Package Management

List Installed Packages:
```
  npm list
```
View Package Version:
```
  npm view package_name version
```