Using animated progressbars is fine for visual users, but more often than not, screen readers remain silent when your app is in an interstitial (e.g. loading) state. Here is a strategy to prevent that.
Menus & Dropdowns
Web-apps are full of interactive items that show a new container with links and options once you interact with them. A simple user experience pattern, but hard to get right if you want to build it with accessibility in mind
A Single Page Application consists of one single HTML document - anything else is being loaded without ever really navigating off of or reloading the page. This leads to accessibility challenges
What makes web-apps special?
Web applications aim to emulate the experience of native apps by loading and displaying data in an asynchronous fashion ("AJAX"). This lack of full page reloads makes it hard for users of screen readers.
The Demo App "Accessibooks"
Reading about patterns in theory only gets you so far – often times you need a concrete example to learn. This is why Accessibooks SPA exists.