1. Node.js Basics and NPM

INTRODUCTION

Node.js is a runtime environment that allows you to run JavaScript outside the browser (on the server).

npm -v - check node version
//app.js
console.log("Hello, Node.js!");

// run command - node app.js
Output: Hello, Node.js!

NODE.JS MODULE SYSTEM

Node.js module system allows you to organize your code to multiple reusable pieces of modules.

In Node.js, every file is treated as a module.(like in react.js every file treated as component)

• A module can export values (functions, objects, variables, classes, etc.).

• Other modules can import them using require.

1. module.exports- Used to define what a module exposes to other files.

    //math.js
    // Exporting a function
    function add(a, b) {
      return a + b;
    }
   
    // Exporting multiple things as an object
    function subtract(a, b) {
      return a - b;
    }
   
    module.exports = {
      add,
      subtract
    };
   

2. require-Used to import from another module.

    const math = require("./math");  // ./ means local file
   
    console.log(math.add(5, 3));       // 8
    console.log(math.subtract(10, 4)); // 6
   

3. Shorthand: exports

    exports.sayHello = function(name) {
      return `Hello, ${name}`;
    };
   

4. Node wrapper :

   When you create a file in Node.js (say app.js), Node doesn’t run your code directly.
   Instead, it wraps the code inside a special function before executing it.

   This wrapper looks like:

    (function (exports, require, module, __filename, __dirname) {
      // Your actual code lives here
    });
   

NODE PACKAGE MANAGER(npm)

• NPM stands for Node Package Manager.

• It comes installed with Node.js.

• It’s used to:

  1. Install and manage third-party libraries (called packages).

  2. Manage your project dependencies via package.json.

  3. Share your own packages with others (publish to npm registry).

1. package.json

   Every Node.js project uses a package.json file.
   It describes the project and keeps track of dependencies.

    npm init -y   //this command creates out package.json file -y means skip all questions
   

2. Installing packages

    npm install express
   

   • Installs inside node_modules/ (node moules creates automatccally or run npm install )

   • Adds to dependencies in package.json.

3. Dependecy Management

    npm install         # Install all dependencies
    npm install express # Install specific package
    npm uninstall express  # Remove package
    npm update          # Update all packages
    npm outdated        # Check outdated packages
   
    npm list       # List installed packages
    npm view express # Show details about a package
    npm search react # Search packages
   

4. package-lock.json

   • Automatically generated when you install packages.

   • Locks the exact versions installed.

   • Ensures that every developer and server uses the same package versions, avoiding “works on my machine” issues.

5. NPM vs NPX

   • NPM → Installs a package.

   • NPX → Executes a package without installing globally.

INTERVIEW QUESTIONS

1. What is the difference between dependencies and devDependencies in package.json?

   • dependencies → Packages required for the app to run in production.
     Example: express, mongoose.

   • devDependencies → Packages only needed during development.
     Example: nodemon, jest, eslint.

2. Difference between npm and npx?

   • npm → Used to install/manage packages.
     Example: npm install express

   • npx → Used to execute packages without installing them globally.
     Example: npx create-react-app my-app (runs directly without global install).

3. What is package-lock.json and why is it important?

   → See above

   Without package-lock.json, different environments might install slightly different versions, causing bugs.