During an interview, I was asked by my interviewer who wasn't familiar with using Node as a web server (he worked with very niche and old tech). I mentioned that in the project I worked on I use Node.js (Express) as the web server and Handlebars for templates. He asked whether there is a big performance cost to the server when it has to do routing, database calls, etc on top of having to render the pages each time. I've always assumed that it was a negligible cost compared to sending plain HTML since it's essentially just doing string replacements/concatenations beforehand and never gave it much thought, but could anyone explain a bit more about it? I'm aware that the database calls and many other things are done asynchronously, which is why Express is fast, but I'm not too sure about how to answer that question specifically.