For users of the TourCMS tour operator ecommerce platform
TourCMS widgets have always loaded the bulk of their content asynchronously (i.e. the rest of the web page continues to load at the same time), however there page has always waited until the tiny initialisation script has run before it continues with the rest of the page, blocking page rendering momentarily.
Modern browsers now allow for loading of even the initial script asynchronously simply with the addition of the "async" attribute on the widget tag itself.
Our main public facing widget page has been updated to add the async tag and any new widgets generated using the widget wizard have the async tag added automatically:
A "Private browsing" window is the best way to compare, however on a super fast broadband connection the difference may be minimal, it's largely a slight delay/glitch in the main page rendering, in the case of tourcms.com the sidebar appearing.