Express.js

Express.js is a web application framework for Node.js, enables you to build server applications in Node.js

As a backend application, it is the glue between your frontend application and a potential database or other data sources (REST APIs, GraphQL APIs, …)

it is the most popular choice when it comes to building JavaScript backend applications with Node.js.

Express.js

Essentially every Express application is a just a series of routing and middleware function calls.