Display confirmation dialog before exiting/refreshing current page

form-control.js

var processDialog = new YAHOO.widget.Dialog('procDialog', {
  width: '400px',
  height: '350px',
  underlay: 'shadow',
  visible: false,
  modal: true,
});

window.onbeforeunload = (function() {
  if ( processDialog.cfg.getProperty('visible') && 
       YAHOO.util.Dom.inDocument('actionMode') && 
       YAHOO.util.Dom.get('processForm').elements['actionMode'].value != 'view' )
  {
    return 'If you leave now, data you have entered may not be saved.';
  }
});

general.js

var isDataChanged = true;

window.onbeforeunload = (function() {
  if(isDataChanged) {
    //For IE only, Firefox and Chrome browsers have their own message to display
    return 'If you leave now, data you have entered may not be saved.'; 
  }
});