Last time I coded a web application was almost 10 years ago. I used Java/JSP/HTML/CSS etc. I've been coding non-web applications only ever since. When I look at modern sites now (like this one), I realize how my web development skills are obsolete. Maybe the most obvious "feature" that I wouldn't know how to implement now is the update of elements on the page after user input without having to refresh the whole page (e.g. the voting/downvoting here updates the vote count without reloading the whole page). What are the basic technologies behind this?