Express.js: Simplifying Node.js Web Development

Express.js is a popular web application framework for Node.js. It provides a robust set of features for building web applications and APIs, including routing, middleware, templating, and more. In this article, we’ll take a closer look at what Express is, how it works, and how to use it to build web applications.

What is Express.js?

Express.js is a minimalist web application framework for Node.js. It was originally created in 2010 by TJ Holowaychuk, and has since become one of the most popular Node.js frameworks. Express.js is built on top of Node.js’s built-in HTTP module, and provides a simple API for handling HTTP requests and responses.

One of the key features of Express is its middleware architecture. Middleware functions can be used to modify the request or response objects, perform authentication or validation, or handle errors. Middleware functions can be defined globally for the entire application, or specific to certain routes or endpoints.

Getting Started with Express.js

To get started with Express, you’ll need to have Node.js and npm (Node Package Manager) installed on your machine. Once you have these installed, you can create a new Express.js application using the following command:

$ npm install express-generator -g
$ express myapp
$ cd myapp
$ npm install

This will create a new Express.js application in a directory called “myapp”. The express-generator package is a scaffolding tool for creating new Express.js applications.

Next, you can start the application using the following command:

$ npm start

This will start the application and listen on port 3000 by default. You can open your web browser and navigate to http://localhost:3000 to see the application running.

Routing in Express

Routing is a core feature of Express.js. It allows you to define URL patterns and map them to specific functions or middleware. To create a new route, you can use the express.Router() method.

Here’s an example:

const express = require('express');
const router = express.Router();

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

module.exports = router;

In this example, we’re creating a new router using express.Router(). We’re then defining a route for the root URL (/) using the router.get() method. This method takes two arguments: the URL pattern, and the function to be executed when the URL pattern is matched.

The function passed to router.get() takes two arguments: the request object (req) and the response object (res). These objects contain information about the incoming request and can be used to modify the response that is sent back to the client.

Middleware in Express

Middleware functions are functions that can be executed before or after a route handler function. Middleware functions can be used to modify the request or response objects, perform authentication or validation, or handle errors.

Here’s an example of a middleware function:

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

// Custom middleware function
const myMiddleware = (req, res, next) => {
  console.log('Middleware function called');
  next();
};

app.use(myMiddleware);

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

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

In this example, we’re defining a custom middleware function called myMiddleware. This function takes three arguments: the request object (req), the response object (res), and the next function. The next function is a callback function that tells Express.js to move on to the next middleware function in the chain.

We’re then using the app.use() method to add myMiddleware to the middleware chain. This means that every incoming request will go through myMiddleware before reaching the route handler function.

Templating in Express

Express.js also provides support for server-side templating. Templating allows you to generate HTML dynamically based on data from your application or database.

There are many templating engines available for use with Express.js, including EJS, Pug (formerly Jade), Handlebars, and Mustache. Here’s an example of how to use the EJS templating engine with Express.js:

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

// Set EJS as the default templating engine
app.set('view engine', 'ejs');

// Define a route that renders an EJS template
app.get('/', (req, res) => {
  const data = {
    title: 'My Page Title',
    message: 'Hello World!'
  };
  res.render('index', data);
});

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

In this example, we’re using the EJS templating engine by setting it as the default engine with app.set('view engine', 'ejs'). We’re then defining a route that renders an EJS template using the res.render() method.

The res.render() method takes two arguments: the name of the template file (without the file extension), and an object containing data to be passed to the template. In this example, we’re passing an object with a title and message property to the index.ejs template.

Conclusion

Express.js is a powerful web application framework for Node.js. It provides a robust set of features for building web applications and APIs, including routing, middleware, templating, and more.

In this article, we’ve covered some of the basics of Express.js, including routing, middleware, and templating. With this knowledge, you should be able to start building your own web applications using Express.js.