How to get info on what key was pressed on for how long?

Imagine this code:

if (navigator.appName == "Opera")
    document.onkeypress = function (e) { console.log(e.keyCode); };
else 
    document.onkeydown = function (e) { console.log(e.keyCode); };

What it does is pretty obvious, I guess. The problem is, if you hold the key for a long period of time, it will be registered a lot of times. In my app, this is a problem because it makes my app do a lot of unnecessary computing. Is it possible to somehow only get a keypress once, but with info on how long the key was held?