WebWorkers are not a new "feature". The last browser to support it was (on desktop) IE in v10 (4 years ago) and on mobile Android 4.4 (3 years ago). Though that doesn't really matter since you can polyfill it, which obviously does not give you multithreading in those older browsers but it still forces you to think async.
Regarding other APIs, a great number has been available since many years, and any newly introduced API since at least 5 years is either non-blocking or async.
