disable browser scrolling while jQuery UI modal dialog is open

$(formObject).dialog({
 create: function(event, ui) {
  $("body").css({ overflow: 'hidden' })
 },
 beforeClose: function(event, ui) {
  $("body").css({ overflow: 'inherit' })
 }
});

Or as I allude to in the comment below:

var dialogActiveClassName="dialog-active";
var dialogContainerSelector="body";

$(formObject).dialog({
 create: function(event, ui) {
   $(dialogContainerSelector).addClass(dialogActiveClassName);
 },
 beforeClose: function(event, ui) {
   $(dialogContainerSelector).removeClass(dialogActiveClassName);
 }
});

But actually to be honest, you should ensure that creating a dialog bubbles an event up to your window object where you’d be watching for said events, roughly something like this pseudo:

var dialogActiveClassName="dialog-active";
var dialogContainerSelector="body";
$(window).on("event:dialog-opened", function(){
    $(dialogContainerSelector).addClass(dialogActiveClassName);
});
$(window).on("event:dialog-closed", function(){
    $(dialogContainerSelector).removeClass(dialogActiveClassName);
});