What is Express JS?

The original author, TJ Holowaychuk, described it as a Sinatra-inspired server.

Web Applications

• Express JS is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

APIs

• With a myriad of HTTP utility methods and middleware at your disposal, creating a robust API is quick and easy.

Performance

• Express JS provides a thin layer of fundamental web application features, without obscuring Node.js features that you know and need.
• Minimal features but many features available via plugins.
• Express JS most important feature is routing.
• Express JS is high performance, extensible framework and can reusable.

Frameworks

• Many popular frameworks are based on Express JS.
• Designed for developing web applications and RESTful APIs.

Ex: several popular Node.js frameworks are built on Express JS.

• Feathers: Build prototypes in minutes and production ready real-time apps in days.
• ItemsAPI: Search backend for web and mobile applications built on Express and Elasticsearch.
• KeystoneJS: Website and API Application Framework / CMS with an auto-generated React.js Admin UI.
• Poet: Lightweight Markdown Blog Engine with instant pagination, tag and category views.
• Kraken: Secure and scalable layer that extends Express by providing structure and convention.

What is Express JS used for?

Express JS is a Node.js web application server framework, designed for building single-page, multi-page, and hybrid web applications. It is the de facto standard server framework for node. It has become the standard server framework for node.js. Express is the backend part of something known as the MEAN stack.

It helps in fast-tracking development of server-based applications. The Express JS framework makes it very easy to develop an application which can be used to handle multiple types of requests like the GET, PUT, and POST and DELETE requests.

Ex: We can use a database like MangoDB with Mangoose to provide a backend for Node.js application. Then Express JS basically helps to manage everything, from routes, to handling requests and view.

Express JS Features

Rapid Server-Side Programming

Being a Node.js framework, Express.js packages many of the commonly used Node.js features, into functions that can be easily called anywhere on the program. As a result, complex tasks that would otherwise take a Node Developer several hundred lines and several hours to program can easily be done by Express JS developers in just a few lines of code and within a few minutes. Express web application development is therefore much quicker than pure Node.js development.

Routing

Routing allows a web application to preserve web page states through their URLs. These URLs may be shared with other users, and visiting these URLs will take users to the exact page state that was originally shared. Node.js has a routing mechanism, but it's a basic and rudimentary one. Express JS offers a more advanced and efficient routing mechanism that is able to handle highly dynamic URLs.

Debugging

All developers encounter bugs with every project that can cause entire applications to malfunction, and one of the most critical tasks of developers is identifying the source of these bugs and correcting them in the quickest possible time. Fortunately, Express.js provides an easy debugging mechanism to allow developers to quickly pinpoint which part of the applications causes bugs.

Templating

Express.js provides a templating engine that allows web pages to have dynamic content by constructing HTML templates on the server side, replacing dynamic content with their proper values, and then sending these to the client side for rendering. In addition to enabling dynamic content, it also takes a significant load from the client side which may have highly variable hardware specifications, and as such, it can make application more efficient.

Middleware

Express.js uses middleware to systematically arrange different function calls. A middleware is a chunk or cluster of code that has access to a user’s request, the application’s response, and the next middleware to be used. With such an architecture, it becomes easy for Express.js developers to add, remove, or modify various features to and from the application, giving high scalability to the application.