Node.js Cheat Sheet

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

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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
  

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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/');
    });
  

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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);
  

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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):

  1. Install dotenv:

      npm install dotenv
     

  2. Load Environment Variables:

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

  3. .env file example:

      PORT=3000
     

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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();
  

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Working with APIs (HTTP Requests)

• Using Axios:

  1. Install Axios:

      npm install axios
     

  2. 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));
  

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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);
    });
  

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Debugging

• Run with Debugger:

    node --inspect-brk app.js
  

• Using console.log() for Debugging:

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

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Package Management

• List Installed Packages:

    npm list
  

• View Package Version:

    npm view package_name version
  

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