AJAX: Delay for search on typing in form field

On my website I use JavaScript/AJAX to do the search and show results while the user is still typing.

HTML (body):

<form action="" method="post" accept-charset="utf-8">
    <p><input type="text" name="q" id="q" value="" onkeyup="doSearch(this.value)" /></p>
</form>

JavaScript (header):

function doSearch(text) {
    // do the ajax stuff here
    // call getResults.php?search=[text]
}

But this could cause a lot of requests coming to the server.

Thus I want to relieve the server by setting up a delay:

Whenever the onkeyup event is fired, the function doSearch() should show an "ajax loading graphic" and wait for 2 seconds. Only if the event is NOT fired again during these 2 seconds, the results should be fetched from the PHP file.

Is there any way to do this? Could you help me please? Thanks in advance!

var delayTimer;
function doSearch(text) {
    clearTimeout(delayTimer);
    delayTimer = setTimeout(function() {
        // Do the ajax stuff
    }, 1000); // Will do the ajax stuff after 1000 ms, or 1 s
}

Simply setup the delayed invocation with setTimeout(), then remove it again on every event with clearTimeout()

HTML

<form action="" method="post" accept-charset="utf-8">
    <p><input type="text" name="q" id="q" value="" onkeyup="doDelayedSearch(this.value)" /></p>
</form>

Javascript

var timeout = null;

function doDelayedSearch(val) {
  if (timeout) {  
    clearTimeout(timeout);
  }
  timeout = setTimeout(function() {
     doSearch(val); //this is your existing function
  }, 2000);
}

For this type of thing I tend to use a cunning little 'throttling' function created by Remy Sharp:

http://remysharp.com/2010/07/21/throttling-function-calls/