A back-end web developer is responsible for server-side web application logic and integration of the work front-end web developers do. Back-end developers usually write web services and APIs used by front-end developers and mobile application developers.
A single-page application (SPA) is a web Application or website that interacts with the user by dynamically rewriting the current web page with new data from the web server, instead of the default method of the browser loading entire new pages. The goal is faster transitions that make the website feel more like a native app.
Progressive web apps (PWA) has in combination of the best features of the site and mobile application built-in it. In practice, this means that such a site can be accessed by users as well as the application and the most interesting thing is an Internet connection is not necessary for this. The installation process can be done in one click directly from the browser.