How to Create Index.js File in Node?

For a long time, JavaScript has only been thought of as a client-side programming language. But the introduction of Node.js, a JavaScript runtime environment capable of executing JavaScript codes outside of the browser changed the game. 

Node.js is now an essential part of building modern applications in the JavaScript ecosystem. Frontend frameworks such as React, Vue, Angular, and React Native use Node.js under the hood for building fast and scalable applications. Check here for Node.js Certification and get started! 

Getting to know how Node.js is used to build backend applications is something that you must do to establish yourself in the JavaScript world. In this article, you will learn how to create an index.js file using Node, node index.js command, and examples. So, if you're ready, then let's jump into the tutorial... 

What is Node Index.js?

What's Node.js, it is a cross-platform back-end JavaScript runtime environment that runs on the V8 engine and executes JavaScript code outside the browser. 

What about node Index.js? Index of Node.js is the file that runs initially once the Node.js code is executed.

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It is responsible for your application's startup, routing, and other functions. Other modules, such as Express, Mongoose, Axios, and others, are used in adding functionalities to a Node.js app. 

How to Create Index.js In Node? Step-by-Step

When you visit most domains, the index files are the first to be served. For instance, visiting the homepage of an HTML or PHP site will take you to the index file. The same concept is used with Node.js, but in Node, using index.js is optional. You can always change the name to something else, such as main.js or app.js instead. All you need to do is make the necessary references in the routing component. 

It is simple to create an Index.js file in Node.js. To create your first Nodejs index file, follow the steps below. 

Here are the steps that you’ll follow to create an index.js file: 

• Head to the Node.js website, download, and install the node package file. 
• Create a new project folder in your working directory. 
• Navigate to the project's location on your terminal and run npm init -y. The above command will produce a package.json file with the codes below inside of it.

{ 
  "name": "nodejs", 
  "version": "1.0.0", 
  "description": "", 
  "main": "index.js", 
  "scripts": { 
    "test": "echo \"Error: no test specified\" && exit 1" 
  }, 
  "keywords": [], 
  "author": "", 
  "license": "ISC" 
}

• Open the project on a code editor such as sublime or vs code. 
• Create an index.js file inside your project folder. 
• Paste the codes below within the index.js file.

const http = require("http"); 
//create a server object: 
http 
  .createServer(function (req, res) { 
    res.write("<h1>Hello World!</h1>");  
    //write a response to the client 
     
    res.end();  
    //end the response 
  }) 
  .listen(8080);  
//Server runs on localhost:8080 

• Run your server on the terminal using node index.js.  
• Visit your browser on localhost:8080. 

Node.js includes an HTTP module that allows you to create a server and serve content to a specific address. We simply created a web server in the code above that writes a heading tag of "Hello World" to the screen and serves it to the localhost:8080 address. When the above code is run through a browser, it yields the following result.

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Node Index.js: Usage

Using Node.js is easy, let's demonstrate its usage by building a simple website that has three pages. The index page, about, and sitemap pages to be precise. 

Example 1: Building a simple website

Follow the steps below to build a simple website using Node.js, we will be including the CSS which will be imported from a content delivery network (CDN). 

Step 1: Create a new project folder and run the code below via the terminal. Make sure you change your directory to this project folder. 

npm init -y 

Step 2: Install Express, a Node.js web application framework that offers many features for building web and mobile applications. 

npm install --save express 

Step 3: Copy and paste the codes below inside the index.js file. 

// Import essential libraries 
const express = require('express'); 
const app = express(); 
const path = require('path'); 
const router = express.Router(); 
// Setup essential routes 
router.get('/', function(req, res) { 
    res.sendFile(path.join(__dirname + '/index.html')); 
    //__dirname : It will resolve to your project folder. 
}); 
router.get('/about', function(req, res) { 
    res.sendFile(path.join(__dirname + '/about.html')); 
}); 
router.get('/sitemap', function(req, res) { 
    res.sendFile(path.join(__dirname + '/sitemap.html')); 
}); 
//add the router 
app.use('/', router); 
app.listen(process.env.port || 3000); 
console.log('Running at Port 3000'); 

The router object was gotten from the Express framework we recently installed. It lets us specify which location we want certain files and codes to execute. 

Step 4: Create an index.html file and paste the following codes inside. The codes also include a bootstrap CDN link that solves all our CSS styling needs. 

<html> 
<head> 
    <title>Express HTML</title> 
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script> 
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap.min.css"> 
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap-theme.min.css"> 
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/js/bootstrap.min.js"></script> 
</head> 
<body> 
    <div style="margin:100px;"> 
        class="navbar navbar-inverse navbar-static-top"> 
        <div class="container"> 
            <a class="navbar-brand" href="/">Express HTML</a> 
            <ul class="nav navbar-nav"> 
                <li class="active"> 
                    <a href="/">Home</a> 
                </li> 
                <li> 
                    <a href="/about">About</a> 
                </li> 
                <li> 
                    <a href="/sitemap">Sitemap</a> 
                </li> 
            </ul> 
        </div> 
        </nav> 
        <div class="jumbotron" style="padding:40px;"> 
            <h1>Hello, world!</h1> 
            <p>This is a simple hero unit, a simple jumbotron-style component for calling extra attenion to featured content or information.</p> 
            <p><a class="btn btn-primary btn-lg" href="#" role="button">Learn more</a></p> 
        </div> 
    </div> 
</body> 
</html>

Note that all the CSS classes such as the “btn, btn-primary, btn-lg" are all coming from the imported CSS files. 

Step 5: Run the code on the terminal using node index.js, then view it on the browser via localhost:3000. See the image below. 

Example 2: Get web resources using Axios

Here is another way to use the index.js file in NodeJs. Let’s use Axios to retrieve a bulk of users from the Jsonplaceholder website. 

NodeJs has a native HTTPS module that can help you make API calls online, but Axios is fantastic, and its usage is effortless. Also, many developers out there use it as their number one package for all things related to making API calls. To use it, follow the steps below: 

Step 1: Open the terminal on your project directory. 

Step 2: Run npm install Axios on the terminal to install the package. 

Step 3: Create an index.js file in the root folder of your project and paste the codes below it. 

// import axios 
const axios = require('axios'); 
// Specify a resource location 
const resourse = 'https://jsonplaceholder.typicode.com/users'; 
axios 
  .get(resourse) 
  .then(users => console.log(users)) 
  .catch(error => console.log(error));

Step 4: Run node index.js on your terminal and observe the result, see the image below.

Example 3: Building a countdown timer 

Here is another usage of index.js in Node.js, let’s build a timer to countdown every second starting from 50. 

let time = 50; 
let countdown = setInterval(update, 1000); 
function update() { 
    let min = Math.floor(time / 60); 
    let sec = time % 60; 
   
    console.log(`${min}:${sec}`); 
    time--; 
   
    if (min == 0 && sec == 0)        
      clearInterval(countdown); 
}

Node Index.js: Implementation

We have one more surprise for you on how to create an index.js in Node.js, and this time it's through a package called create-index. If you want to build an ES6 module package and you want to quickly bundle the files before shipping them online, the `create-index` package will be very helpful to you. How do you use it? Follow the steps below:

Step 1: Run npm install create-index to install the package to your project.

Step 2: Create an index entry file by running this command npx create-index ./ on the terminal.

The above command will create an index.js file and add a line of code as can be seen in the snippet below: 

// @create-index 

Step 3: Create the files to be included for export. These files are the once you intend on pushing together as one package. Create them at the root of the project, you write all your logic, classes, and functions in these files. You can use the command below: 

touch foo.js bar.js baz.js 

The above code should all be lined up similar to the block below: 

./ 
  - bar.js 
  - baz.js 
  - foo.js 
  - index.js 

Step 4: Bundle them up by running npx create-index ./ once again on the terminal, and you will have a result similar to the one in the image below. 

How to Ignore Files on –update?

For many reasons, you may want to exclude some files from being listed in the index.js file. To achieve this, change the comment on the index.js file to the one seen in the block below: 

//  @create-index {"ignore": ["/baz.js$/"]} 

Next, run npx create-index --update ./index.js on the terminal and the result should look like the one below:

And there you have it with how to create an index.js in Node.js. 

Why is Index JS File Important in Node JS? 

The index.js file holds significant importance in Node.js applications as it typically serves as the entry point of the application. Node js will look for a file named index js within the module directory by default when a module is required. Following this it simplifies the module loading process, as developers don't need to specify the exact filename when importing a module. 

Furthermore, this file is often used to organize and centralize the exports of a module. Developers can import various functions, classes, or constants from other files into index.js and then export them from there. This practice allows other parts of the application to access multiple exports from a single module through a single import statement, thereby promoting cleaner and more maintainable code. 

Thus index.js in Node.js plays a crucial role in module management and application structure, acting as a default entry point and a central hub for module exports, which aids in code organization and simplicity. 

Best Practices for Index JS File in Node JS 

1. Entry Point Clarification:

   Use index.js as the clear entry point of your Node.js application or module. This establishes a standard starting point for the code, enhancing readability and maintainability. 

2. Export Centralization:

   Aggregate exports from various parts of your module in index.js. This allows other modules to import multiple functionalities from a single location, simplifying the import statements. 

3. Minimal Logic:

   Keep index.js focused on imports and exports. Avoid embedding significant application logic in this file to maintain clarity and separation of concerns. 

4. Documentation:

   Comment on your index.js file to explain its role in the module or application. This is especially helpful in larger projects to guide new developers. 

5. Require Order:

   Organizing requires logic. Group standard library imports, third-party module imports, and internal module imports separately for easy identification. 

6. Error Handling:

   Include basic error handling for module loading if your application's startup process is complex. 

7. Performance Considerations:

   Be mindful of what is included or required in index.js, as unnecessary imports can impact startup time and overall performance. 

8. Consistency:

   Maintain a consistent structure and style in index.js files across different modules in larger projects. This uniformity aids in understanding and navigating the codebase. 

9. Testing:

   If index.js includes some logic or configuration, ensure it is covered by tests to avoid startup issues. 

10. Use of index.js in Larger Apps:

    In larger applications, index.js can be used to set up global configurations or middleware, but keep it minimal and delegate specifics to appropriate modules.

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Conclusion

We have come to the end of this tutorial, hopefully, you got some understanding of how to create index.js files in Node.js. The index.js file in Node.js projects plays a pivotal role as both an entry point and a central hub for module management. Best practices for index.js emphasize its use for organizing and centralizing exports, thereby streamlining the import process across the application. Keeping index.js clear of complex logic and focusing primarily on imports, exports, and minimal configurations ensures clarity and maintainability. Adequate documentation, logical organization of requirements, and consistent structure across modules further enhance the readability and navigability of the codebase. By adhering to these best practices, developers can leverage the index.js file to create a more efficient, maintainable, and scalable Node.js application, ultimately leading to better project organization and easier code management in both small and large-scale projects.  We have a ton more tutorials like this one on upGrad.

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