Querying a page without reloading current page

Is there a way in javascript to capture the onKeyUp event and send a message to the server (I assume by requesting another page) and not reload the current page? Also, a while back I had to do something (can't even remember what now), but it resulted in a page reloading every few seconds. At first we thought this was fine, but when we turned our speakers on, we heard a click every time it reloaded. In this particular case, I wouldn't want a click to happen every time someone types something. Any suggestions? Thanks.