PUBLIC MARKS with tags polyfill & js

The global fetch function is an easier way to make web requests and handle responses than using an XMLHttpRequest.

The polyfill service selectively bundles browser polyfills based on the User-Agent header supplied in a request, with the intention of allowing JavaScript and CSS developers to use modern standards in legacy user agents that do not natively support the standard.

test whether a CSS media type or media query applies

In your animation work, you've used a timer loop to make changes every few milliseconds. Good for us: browser vendors have decided, "hey, why don't we just give you an API for that, because we can probably optimize some things for you." So it's basic API for use with animation, whether that be DOM-based styling changes, canvas or WebGL.

Look up HTML5 features, know if they are ready for use, and if so find out how you should use them – with polyfills, fallbacks or as they are