Use onevent attribute. It must point to a callback function reference (so don’t include parentheses!):
<f:ajax ... onevent="functionName" />
Whereby the actual callback function look like this (JSF will provide the argument all by itself):
function functionName(data) {
var status = data.status; // Can be "begin", "complete" or "success".
var source = data.source; // The parent HTML DOM element.
switch (status) {
case "begin": // Before the ajax request is sent.
// ...
break;
case "complete": // After the ajax response is arrived.
// ...
break;
case "success": // After update of HTML DOM based on ajax response.
// ...
break;
}
}