Node JS

What is NODE JS

Browser can only undersntand HTML , CSS and JavaScript
That means to run JavaScript we need a browser
But what if we want to run JavaScript out of the browser , then we need a runtime environment that is able to perfrom memory management , event handling and other tasks
For this purpose we use Node JS

NODE JS

Node js is a runtime environment that helps to run javaScript ouf of the browser
But why do we need to run javascript out of the browser
- What if we are writing a server side code that is in JavaScript , then we need NODE js to be installed on that server as well
- What is a server
  - A server is basically a computer that has extreme processing capabilites like huge amoung of RAM , SDD
  - Hence if we are using js to manage the server then to undersntand JS we need a runtime environment which is node js
Why is it called as NODE ?
- Node.js is called "Node" because it was designed to be a scalable, event-driven system that can serve as a "node" in a network, handling numerous connections simultaneously
Even in the logo itselsf it says`` RUN JAVASCRIPT EVERYWHERE

When you INSTALL node what all gets installed

When you install Node.js locally, typically through an official installer or a package manager, several components and tools are installed. Here’s an overview of what gets installed:

1. Node.js Runtime

Node.js Binary: The core executable that runs JavaScript code outside of a browser environment.
Built-in Libraries: Standard libraries that come with Node.js, such as fs (file system), http, path, and more.

2. npm (Node Package Manager)

npm Binary: The command-line tool for managing JavaScript packages.
Node_modules Directory: A folder where installed packages and their dependencies are stored. This directory is created inside your project directory when you install packages.

3. Core Utilities

npx: A package runner tool that comes with npm. It allows you to execute binaries from npm packages without installing them globally.
Node-gyp: A cross-platform command-line tool written in Node.js for compiling native addon modules for Node.js.

4. Configuration Files

package.json: A file that holds metadata relevant to the project and lists the dependencies. It is created when you run npm init.
package-lock.json: Automatically generated for any operations where npm modifies either the node_modules tree or package.json. This file ensures that installs are repeatable and predictable.

Node Package Manager

npm, which stands for Node Package Manager, is a crucial tool for managing JavaScript packages and dependencies. It is installed automatically when you install Node.js. Here’s a detailed overview of what npm is and what it does:

Key Features and Functions of npm

Package Management:
- Install Packages: You can install JavaScript libraries and frameworks from the npm registry into your project. For example, to install the express package:
```
  npm install express
```
- Uninstall Packages: To remove an installed package:
```
  npm uninstall express
```

By default the node terminal is configured to look up repository in https://registry.npmjs.org/
We can set a custome registry as well :
```
  npm config set registry https://custom-registry.example.com/
```
npm config set registry https://custom-registry.example.com/
Dependency Management:
- package.json: This file lists the dependencies and metadata of your project. When you run npm install, npm reads this file to determine which packages to install.
- package-lock.json: This file ensures that installs are repeatable and consistent across different environments by locking the versions of installed packages.
Script Management:
- You can define scripts in your package.json to automate common tasks, such as running tests or starting your application. For example:
```
  "scripts": {
    "start": "node app.js",
    "test": "mocha"
  }
```
- To run a script:
```
  npm run start
```
Global vs. Local Installation:
- Local Installation: Installs the package into the node_modules directory within your project. These packages are accessible only within the project.
```
  npm install express
```
- Global Installation: Installs the package system-wide, making it accessible from any project. Useful for command-line tools.
```
  npm install -g nodemon
```
Publishing Packages:
- You can publish your own packages to the npm registry for others to use. To publish a package:
```
  npm publish
```
- Before publishing, you need to create an account on the npm website and log in using:
```
  npm login
```

Commonly Used npm Commands

Initialize a Project:
```
  npm init
```
This command creates a package.json file with project details.
Install All Dependencies:
```
  npm install
```
Installs all packages listed in the package.json.
Update Packages:
```
  npm update
```
Updates all the packages to the latest version respecting the version ranges specified in package.json.
List Installed Packages:
```
  npm list
```
Lists all installed packages and their dependencies.
Check for Outdated Packages:
```
  npm outdated
```
Shows a list of packages that are outdated.
Audit Packages for Vulnerabilities:
```
  npm audit
```
Runs a security audit and provides a report of vulnerabilities in the dependencies.

Example Workflow

Create a new project directory and initialize npm:
```
 mkdir my-app
 cd my-app
 npm init -y
```
Install Express and Save to Dependencies:
```
 npm install express --save
```

Create a simple app.js file:

 // app.js
 const express = require('express');
 const app = express();
 const port = 3000;

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

 app.listen(port, () => {
   console.log(`App listening at http://localhost:${port}`);
 });

Add a start script to package.json:

 "scripts": {
   "start": "node app.js"
 }

Run the application:
```
 npm run start
```