apex:actionFunction javascript
<apex:actionFunction name="clearFormFn" action="{!clearForm}" status="overlayStatus" rerender="{!$Component.myForm}" />
<apex:actionStatus id="overlayStatus" onstart="showOverlay();" onstop="hideOverlay();"/>
public void clearForm()
{
//more code here....
}
<div id="overlay"></div>
<script type="text/javascript">
Sfdc.onReady(function()
{
SfdcApp && SfdcApp.Visualforce && SfdcApp.Visualforce.VSManager && SfdcApp.Visualforce.VSManager.vfPrepareForms(["myPage:myForm"]);
});
</script>
<script type="text/javascript">
//---------------------------------
// Function to display overlay div
//---------------------------------
function showOverlay() {
var o = document.getElementById('overlay');
o.style.visibility = 'visible';
//create inner div
var i = document.createElement('div');
i.id = 'overlayInner';
i.style.position = "fixed";
i.style.top = (o.clientHeight)/2 + 'px';
i.style.left = (o.clientWidth)/2 + 'px';
//append inner div inside overlay div
o.appendChild(i);
}
//---------------------------------
// Function to hide overlay div
//---------------------------------
function hideOverlay() {
var o = document.getElementById('overlay');
o.style.visibility = 'hidden';
}
</script>
!= null or !isEmpty() ? find the object name by passing id