The Web is fundamentally designed to work for all people, whatever their hardware, software, language, culture, location, or physical or mental ability.
“Letting a website know you’re using a screen reader means running around the web waving a red flag that shouts “here, I’m visually impaired!”… It would take away the one place where blind people can be relatively undetected without our white cane or guide dog…and therefore giving others a chance to treat us like true equals.”Marco Zehe: Why Screen Reader Detection is a Bad Thing
elem.scrollTop, other scrolly things
...and much more. Use sparingly while loading.
Everything you customize has to be sent over the wire.
Prioritize accessible interactions.
Load the same app from both the server and client