Express JS Routing

Last Updated: 22nd June, 2023

Introduction

Routing is the process of mapping a URL to a specific piece of functionality within a web application. In other words, when a user requests a specific URL, the server needs to know how to handle that request and what data to send back to the client.

Express.js is a popular web application framework for Node.js that provides a simple and flexible way to handle routing. With Express.js, you can define routes for your web application that map URLs to specific actions or functionality.

In Express.js, routing is handled using a combination of HTTP methods (such as GET, POST, PUT, DELETE, etc.) and URL patterns. You define routes using these HTTP methods and URL patterns, and then specify the function or functions that should be executed when that route is accessed.

Routing is a critical part of any web application, and Express.js makes it easy to define and handle routes with its flexible and powerful routing system. With Express.js, you can build complex web applications that handle multiple routes, parameters, and middleware functions with ease.

Basic routing in Express.js

Express.js provides a straightforward and intuitive way to define routes for your web application. In this section, we will cover the basics of routing in Express.js.

To define a route in Express.js, you need to specify an HTTP method and a URL pattern that matches the request. You can do this using the app.METHOD() functions, where METHOD is the HTTP method you want to handle (such as get, post, put, delete, etc.).

For example, to define a route that handles GET requests to the root URL ( / ), you can use the following code:

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

This code defines a route for the root URL ( / ) that handles GET requests. When a user navigates to the root URL, Express.js will call the function specified as the second argument to app.get(). This function takes two arguments: req (short for request) and res (short for response). The req object contains information about the incoming request, such as headers and parameters, while the res object is used to send a response back to the client.

In this case, the function simply sends the string 'Hello World!' back to the client using the res.send() method.

You can also define routes that include parameters. For example, to define a route that handles GET requests to a URL like /users/:userId , where userId is a dynamic parameter, you can use the following code:

app.get('/users/:userId', function (req, res) {
  res.send('User ID: ' + req.params.userId);
});

In this code, the:userId portion of the URL specifies a dynamic parameter that can be accessed using the req.params object. When a user navigates to a URL that matches this pattern (such as /users/123), Express.js will call the function specified as the second argument to app.get(), passing in the req and res objects as before. The function then uses the req.params object to retrieve the value of the userId parameter and sends it back to the client using res.send().

In addition to app.get(), Express.js provides similar methods for handling other HTTP methods such as POST, PUT, and DELETE. You can use these methods to define routes for your web application that handle different types of requests and perform different actions depending on the request.

Overall, basic routing in Express.js is simple and straightforward and provides a powerful way to handle requests and define functionality for your web application.

Route handlers and middleware functions

In Express.js, route handlers are functions that are executed when a specific route is requested by a client. Middleware functions, on the other hand, are functions that are executed before or after route handlers and can modify the request or response objects, perform authentication, logging, or any other custom task.

To define a route handler in Express.js, you simply pass a callback function to the app.METHOD() function. For example, to define a route handler that handles GET requests to the root URL (/), you can use the following code:

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

In this code, the callback function takes two arguments: req (short for request) and res (short for response). The req object contains information about the incoming request, such as headers and parameters, while the res object is used to send a response back to the client.

Middleware functions, on the other hand, are functions that can be called before or after a route handler to perform additional processing or modify the request or response objects. Middleware functions can be defined using the app.use() function, which takes a callback function as its argument.

For example, to define a middleware function that logs the incoming request to the console, you can use the following code:

app.use(function (req, res, next) {
  console.log('Incoming request: ' + req.url);
  next();
});

In this code, the middleware function takes three arguments: req, res, and next. The req and res objects are the same as in a route handler, while next is a callback function that must be called to move on to the next middleware function or route handler in the chain.

To use multiple middleware functions for a route, you simply chain them together using the app.use() function. For example, to use the logging middleware function defined above and another middleware function that performs authentication, you can use the following code:

app.get('/dashboard', function (req, res) {
  res.send('Welcome to your dashboard!');
});

app.use('/dashboard', function (req, res, next) {
  // Perform authentication
  next();
});

app.use(function (req, res, next) {
  console.log('Incoming request: ' + req.url);
  next();
});

In this code, the second middleware function performs authentication before the route handler for /dashboard is called. The first middleware function defined earlier is used for all routes and will be executed for this route as well.

Overall, route handlers and middleware functions are a powerful and flexible way to handle requests and define functionality for your web application in Express.js. By separating your code into modular pieces, you can build complex applications that are easy to manage and maintain.

Express.js routing options and features

Express.js provides a range of routing options and features that make it a powerful and flexible framework for building web applications. Here are some of the key routing options and features in Express.js:

1. HTTP Verbs: Express.js supports all HTTP verbs, including GET, POST, PUT, DELETE, and more. You can use these verbs to define different routes for different types of requests.
2. Route Parameters: Express.js allows you to define routes with parameters, which can be used to extract values from the request URL. For example, you can define a route like /users/:id to extract the id parameter from the request URL.
3. Route Handlers: Express.js allows you to define route handlers, which are functions that are executed when a specific route is requested. You can use route handlers to handle requests, render views, and perform other tasks.
4. Middleware: Express.js provides middleware, which are functions that are executed before or after route handlers. Middleware functions can be used to perform tasks like authentication, logging, and error handling.
5. Routing Methods: Express.js provides routing methods, which are functions that correspond to HTTP verbs. You can use routing methods like app.get(), app.post(), app.put(), and app.delete() to define routes for different types of requests.
6. Route Chaining: Express.js allows you to chain multiple route handlers and middleware functions together for a single route. This makes it easy to define complex routes that perform multiple tasks.
7. Route Groups: Express.js allows you to group related routes together using the Router object. This makes it easy to define routes for different parts of your application and keep your code organized.
8. Route Parameters Validation: Express.js allows you to validate the values of the parameters in the request URL using various libraries like Joi and Express-validator.
9. Route Modularization: Express.js allows you to modularize your routes and middleware functions into separate files, making your code more organized and maintainable.
10. Error Handling: Express.js provides error-handling middleware that can be used to handle errors that occur during the request/response cycle. You can use this middleware to handle errors like 404 Not Found, 500 Internal Server Error, and others.

These are some of the key routing options and features in Express.js. By using these features effectively, you can build powerful and flexible web applications with ease.

Conclusion

In conclusion, Express.js is a popular web application framework for Node.js that provides a simple and flexible way to handle routing. With Express.js, you can define routes for your web application that map URLs to specific actions or functionality.

Express.js provides a powerful way to handle requests and define functionality for your web application. The basic routing is simple and straightforward. Additionally, you can use middleware functions to perform additional processing or modify the request or response objects. Overall, Express.js provides a flexible and robust routing system for building complex web applications.