How to call a function every hour?

Question

I am trying to update information from a weather service on my page. The info should be updated every hour on the hour. How exactly do I go about calling a function on the hour

Answer 1

EDIT: Oops, I didn't see the " o' clock" things, so I edit my answer :

var last_execution = new Date().getTime();
function doSomething(force){
  var current_time = new Date().getTime();
  if (force || (current_time.getMinutes() == 0)
  {
    last_execution = current_time;
    // something
    // ...
  }
  setTimeout(doSomething(false), 1000);
}
// force the first time
doSomething(true);