What Is the Express Node.js Framework?


In this blog, we'll learn about the Express free and open-source Node.js web application framework.  It’s built on top of the Node.js built-in HTTP module, Express benefits us set up routing and handle the request/response cycle.

In this Blog we will see and take a look at some of the features of Express, absorb what it can offer us that the built-in HTTP modules in Node.js can't, and explain why it's a great tool in any Node developer's toolbox.


Understand the benefits of working with a web framework like Express

Identify core components that make up the Express framework and the Node.Js expertise.


Learn how Express uses middleware to extend its capabilities

Express.js overview


The most common use for Node.js is writing Web applications and a large percentage of these webs applications today are using Express.js as their server framework. Express can be used to create JSON APIs, Server-side rendered web applications, or Microservices.


According to the Express website itself, Express is a "Fast, unopinionated, minimalist web framework for Node.js". In our own words, Express (and the other web frameworks in the Node.js ecosystem) makes developing and maintaining a web server much friendlier than doing it using built-in Node.js utilities.

Express uses those built-in utilities under the hood, but provides you with a set of common handlers, settings, utilities, and other tools which greatly improve the experience and speed of creating a web server. The Express framework comes with the basics of what you need to get started, and doesn't impose any strict rules on how you use those tools to create your application.


The the community-supported ecosystem around Express provides countless extensions in the form of "middleware" (more on that later) to add any kind of functionality or help you accomplish just about any task you might want. This combination of sane defaults and common tools combined with the rich ecosystem is what has made Express the most popular server framework for Node.js.


Core concepts in Express.js

Most web servers do something like the below.

1.      Listen for requests that come to the server

2.      Receive HTTP requests at an endpoint, such as /home, and parse the information sent with the request

3.      Run code in response to the type of HTTP verb, the request was made from

4.      Respond to the request in some way

When working with Express, we have tools to help us achieve these steps in only a few lines of code. The three big concepts that Express works with areas below.


1.      Routing

2.      Middleware

3.      Request/Response


Routing aims to define what code needs to be run in response to a request that the server received. This is typically done based on the combination of the URL pattern and the HTTP Method associated with the request.

For For example, if a GET request is received for the URL /home, send back the HTML for the homepage. Or if a POST request is sent to /products create a new product listing.

These are the basic building blocks of any API or web application, and Express provides us with flexible ways to define code to handle this request.



Often shortened to req and res, you'll see these everywhere when working with Express and other Node.js server frameworks. They represent the request which was received by the server and the Response which you will eventually send back.

These are based on objects that come built into Node.js, the ClientRequest, and ServerResponse objects -- integral parts of an HTTP transaction.

A single HTTP transaction can be described by the Request and Response cycle.

·         A client sends a request to the server.

·         The server receives the request and reads the data that accompanies it. This includes the headers, the URL path the request is being sent to, the HTTP method used to send the request, query parameters, cookies, the data or payload sent with the request (if any) -- and more.

· the server must send a response back to the client: this involves a status code, headers, content-encoding, any data being returned, and again, many other possible things.

·         Once the server has sent the response back to the client, the HTTP transaction has been completed.

That is a rough explanation of what the Request/Response cycle looks like, but this interaction makes up the core of most HTTP transactions.

Express helps us complete these transactions by helpfully augmenting the built-in Request and Response objects that the Node.js core HTTP module provides when a request is received by your server.




Middleware is code that executes somewhere during the life cycle of the request/response cycle and is commonly used to add functionality or augment the behavior of the webserver. but here is a general overview.

Middleware is functions that have access to the Request and Response objects. They can run any arbitrary code and are executed one after another according to what order the middleware is stacked. Middleware is part of the program that adds some kind of functionality to your application, often by augmenting or adding things to the req and res objects themselves. Middleware can be added to your application without needing to change much.

Express uses Connect style middleware which is a common format for Node.js server frameworks. That means middleware written for Express can also be used in many other frameworks that implement Connect style middleware.

The common middleware used with Express is cookie-parser. It parses the Cookie header of an incoming request and populates the cookie values on the req object under req. cookies as an object. This means that any other route handlers or middlewares that run 


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