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.js. Simply express js is one feature for node js, it can be an API or framework.
Express is the backend part of the MEAN stack, together with MongoDB database and AngularJS frontend framework.
Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. Express provides a thin layer of fundamental web application features, without obscuring Node.js features that you know and love.
Simply ExpressJs is controller for Node.Js like struts action.
Prerequisites: Node should be installed before. And next..
This is the command for installing ExpressJS
npm install express
Express is a routing and middleware web framework with minimal functionality of its own: An Express application is essentially a series of middleware calls.