That works for many scripting capabilities, but there’s plenty you can’t polyfill. If you’re stuck with the old MSHTML-based web view (which you will be on all but very recent Windows 10 and even sometimes there), there are various CSS Grid features that you can’t polyfill, and you’ll have a number of weird and annoying SVG sizing and styling issues quite apart from any potential missing features, and a bunch of other things like that—even if you polyfill everything in reach (which, even where possible, may perform terribly).