How to Build a Basic Web Application with Express JS - Are you looking to build a web application using Node.js and Express? Express is a popular web framework for Node.js that allows you to build scalable and robust web applications quickly and easily. In this article, we will guide you through the process of building a basic web application with Express.

Table of Contents

1. Introduction to Express
2. Prerequisites
3. Installing Express
4. Setting up the project
5. Creating the server
6. Routing
7. Handling requests and responses
8. Adding views
9. Adding static files
10. Error handling
11. Conclusion
12. FAQs

1. Introduction to Express

Express is a minimalist web framework for Node.js that provides a set of features for building web applications. It is designed to be flexible and scalable, allowing you to create applications ranging from small, single-page applications to large, complex systems.

2. Prerequisites

Before we get started with building our web application, there are a few prerequisites that we need to have in place. These include:

• Node.js and npm installed on your machine
• Basic knowledge of JavaScript and Node.js

3. Installing Express

To get started with Express, we need to install it. You can install Express using npm, which is the package manager for Node.js. Open your terminal and run the following command:

npm install express --save

This will install Express and save it as a dependency in your project's package.json file.

4. Setting up the project

To set up our project, we need to create a new directory and initialize it with npm. Open your terminal and run the following commands:

mkdir myapp
cd myapp
npm init -y

This will create a new directory called myapp and initialize it with npm. The -y flag will accept all the defaults for the package.json file.

5. Creating the server

To create the server, we need to create a new file called index.js in the root directory of our project. This file will serve as the entry point for our application. Open your text editor and create a new file called index.js. Add the following code to it:

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

const port = 3000

app.listen(port, () => {
  console.log(`Server running on port ${port}`)
})

This code imports the Express module, creates an instance of the app, and starts the server listening on port 3000. You can change the port number to any number that you like.

6. Routing

Now that we have our server up and running, we can start adding routes to it. Routes are the URLs that the user can visit on our website. To add a route, we use the app.get() method. Add the following code to your index.js file:

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

This code creates a new route for the root URL (/) and sends a response back to the user with the message "Hello World!".

7. Handling requests and responses

When a user visits a URL on our website, the server receives a request from the client and sends a response back. We can handle requests and responses using the req and res objects. The req object contains information about the request, such as the URL and any data sent by the client. The res object is used to send a response back to the client. Add the following code to your index.js file: This code creates a new route for the URL /about and sends a response back to the user with the message "This is the about page". We can also use the res.sendFile() method to send a file back to the user. For example:

app.get('/contact', (req, res) => {
  res.sendFile(__dirname + '/public/contact.html')
})

This code creates a new route for the URL /contact and sends the file contact.html located in the public directory back to the user.

8. Adding views

Views are the templates used to render the content of our web pages. Express uses a view engine to render views. There are many view engines available for Express, but we will use the EJS view engine in this article. To use EJS, we need to install it first. Run the following command in your terminal:

npm install ejs --save

Once EJS is installed, we need to set it as the view engine for our application. Add the following code to your index.js file:

app.set('view engine', 'ejs')

This code sets EJS as the view engine for our application. We can now create a new directory called views and add a file called index.ejs to it. This file will be used to render the content of our home page. Add the following code to your index.ejs file:

<!DOCTYPE html>
<html>
  <head>
    <title>My Website</title>
  </head>
  <body>
    <h1>Welcome to my website</h1>
    <p>This is the home page.</p>
  </body>
</html>

Now we need to update our index.js file to render the index.ejs file when the user visits the home page. Replace the code for the / route with the following:

app.get('/', (req, res) => {
  res.render('index')
})

This code renders the index.ejs file and sends it back to the user.

9. Adding static files

Static files are the files that are served as-is to the user, such as CSS, JavaScript, and images. We can serve static files using the express.static() middleware. To serve static files, we need to create a new directory called public and add our static files to it. Add the following code to your index.js file:

app.use(express.static('public'))

This code tells Express to serve any files in the public directory as static files. We can now add our CSS file to the public directory and link to it in our index.ejs file. Create a new file called style.css in the public directory and add the following code to it:

body {
  background-color: #f1f1f1;
}

h1 {
  color: #444;
}

Now we need to link to the style.css file in our index.ejs file. Add the following code to the head section of your index.ejs file:

<link rel="stylesheet" type="text/css" href="/style.css">

This code links to the style.css file and applies the styles to our web page.

10. Error handling

Finally, we need to add error handling to our application. Express provides a set of error-handling middleware functions that we can use to handle errors. Add the following code to your index.js file:

app.use((req, res, next) => {
  res.status(404).send("Sorry, that page doesn't exist

This code creates a new middleware function that will be called when a request is made to a route that does not exist. The middleware function sets the status code to 404 and sends a message to the user indicating that the page they requested does not exist.

We can also create error-handling middleware functions to handle other types of errors. For example, we can create a middleware function to handle server errors. Add the following code to your index.js file:

app.use((err, req, res, next) => {
  console.error(err.stack)
  res.status(500).send('Something broke!')
})

This code creates a new middleware function that will be called when there is a server error. The middleware function logs the error stack trace to the console and sends a message to the user indicating that something went wrong.

Conclusion

In this article, we have learned how to build a basic web application with Express JS. We have covered topics such as creating a server, handling requests and responses, adding views, serving static files, and error handling. With these skills, you can build a variety of web applications using Express JS.

FAQs

1. What is Express JS? Express JS is a web application framework for Node.js. It provides a set of features for building web applications such as routing, middleware, and templating.
2. What is middleware in Express JS? Middleware in Express JS are functions that are executed in a sequence for every request made to the server. They can modify the request and response objects, perform authentication, handle errors, and more.
3. What is a view engine in Express JS? A view engine in Express JS is a template engine that is used to render dynamic content on the server-side. Express JS supports many view engines such as EJS, Pug, and Handlebars.
4. How do I serve static files in Express JS? You can serve static files in Express JS using the express.static() middleware. This middleware function takes the name of a directory as an argument and serves any files in that directory as static files.
5. How do I handle errors in Express JS? You can handle errors in Express JS using the built-in error-handling middleware functions. You can create custom middleware functions to handle specific types of errors, such as 404 errors or server errors.

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Final Thoughts

Express JS is a powerful framework for building web applications with Node.js. By following the steps outlined in this article, you can get started with building your own web applications using Express JS. Remember to take advantage of the various features provided by Express JS, such as middleware and view engines, to create robust and scalable web applications. With practice and experience, you can become proficient in using Express JS and build even more advanced web applications.

Thank you for reading, and happy coding!