http://code.google.com/apis/analytics/docs/tracking/asyncTracking.htm

The form bit is pretty standard.

<div class="form-row">
<div class="field-label"><label for="field1">Username</label>:</div>
<div class="field-widget"><input name="field1" id="field1" class="text required validate-username" title="Enter yourusername." /></div>
</div>

The Javascript bit included on this page in an external JS file.

Validation.addAllThese([
['validate-username','Sorry, that username is already taken.',function(v,elm) {
if(elm._ajaxValidating && elm._hasAjaxValidateResult) {
elm._ajaxValidating = false;
elm._hasAjaxValidateResult = false;
return elm._ajaxValidateResult;
}
var sendRequest = function() {
new Ajax.Request('/path/to/check/file?username='+v+'&r='+Math.random(),{
onSuccess : function(response) {
elm._ajaxValidateResult = eval(response.responseText);
elm._hasAjaxValidateResult = true;
Validation.test('validate-username',elm);
}
});
elm._ajaxValidating = true;
return true;
}
return elm._ajaxValidating || Validation.get('IsEmpty').test(v) || sendRequest();
}]
]);

The Javascript bit in the page.

<script language="javascript" type="text/javascript">
var valid_register = new Validation('register', {immediate:true,stopOnFirst:true,onSubmit:false});
</script>

The form is submitted with an Event.observe on the submit button I have as well.

And so concludes my first geekish post for a while, it feels strangely good!

The original bugzilla report has the repeatable test case (see comment 4) to test.

A full text case can be found on the Ruby on Rails site. The bug is listed in bugzilla as well. Go vote for bug 357947 to get this sorted.

adaptive path ý ajax: a new approach to web applications