Travis Leithead:
I guess you'd check for URL.href then? Or try { new URL("/test"); } catch (ex) {
console.log("not supported"); }
I agree with Travis, you should be checking the particular features you want to use, rather than checking the existence of the prototype as a proxy for that test.
If URL.prototype was required to exist, you could just do ("href" in URL.prototype). Since it currently doesn't, you could do ("href" in (URL.prototype || {})).
