<script type="text/javascript">
		function start() {
			...
		}
</script>

...

<p:commandButton id="btn" value="Do somthing" 
	update="panel" action="#{userBean.recover}" onclick="start()" 
	widgetVar="startButton" />

<p:progressBar id="progressBarClient" widgetVar="pbClient" />

<p:commandButton id="btn" value="Do somthing" 
	update="panel" action="#{userBean.recover}" oncomplete="start()" 
	widgetVar="startButton" />

private String passwordChanged; // изначально пустое

@Override
	public void run() {
		// do proces
		passwordChanged = "Новый пароль установлен";
}

<p>#{userBean.passwordChanged}</p>

<h:body onload="doLoad()">
	<script language="JavaScript">
	<!--
    // we put this here so we can see something change
    document.write('<b>' + (new Date).toLocaleString() + '</b>');
	//-->
	</script>