Is there any reason your scripts are relying on document.readyState "complete" everywhere instead of "interactive"?
It makes the cart load after all subresources, including all images.
This makes for a very slow cart load, especially for those on mobile.
Why isn't a readyState of "interactive" or the usual jquery-style onReady (DomContentLoaded) event good enough?
I run a store page that is very simple, but does have a good many thumbnails.
Our customer base is 80% mobile tablet users on a mobile network.
If the customer knows what they want, before absolutely every single images loads on the page...
I'd rather they see the side-cart view than the full page cart, which is what happens when the side-cart doesn't load til the very very end.