I haven't used Flask and Django, but I use Express and Node to make my backend. I also use JavaScript frameworks to deploy and make backend servers. Basically, these JavaScript frameworks help us like Node. I can tell you about Node. Node is a Chrome-created JavaScript engine, which has been taken out from your Chrome browser only and wrapped with a JavaScript wrapper in order to make backend services and write JavaScript code as a backend code also. So, Express is a framework which is used in Node.js to create interactive servers and do well in backend.
