I understand why Yarn was started... but given that npm proper supports most of the enhancements that yarn brought in terms of performance, I'm not sure I get yarn's role at this point other than remnant popularity.
Kind of a cool naive approach. Would not use this on very large text or for large collections of strings for the most part, it may be usable as part of a systematic map-reduce algorithm.
Another thing to consider would be creation of word stems converted with phonology for comparison, and a relation score instead of true/false. Which would be closer to what search engines actually do.
It's worth mentioning that there's a search cost for properties in the prototype hierarchy, so doing more than 1-2 inheritance levels is generally a bad idea depending on your use case and performance needs.
Mainly in that maintaining it can become an issue... also, if you exceed a certain size it won't be indexed, so you'll have to reference other sitemap files, and/or generate them. I've found you're far better off ensuring only the recent endpoints that are updated since the last google scan are about best. And even then, google (and bing) will do a good job at natural discovery. The sitemap really only allows for those sites with frequent publication to be checked more often by google. If you are doing less than a couple posts a day, there's very little reason to worry about it.
When creating a site with ads, wrap your placeholder with an "ad" class, and define the demensions. Also, make sure that it renders well with `.ad { display:none !important;}` set so that you work well with ad blockers.
When working on injecting ads/content, don't use heavy frameworks like jquery, stick to micro frameworks or preferably hand-craft what you need and use rollup to build/bundle. http://microjs.com/ is your friend on this one. If you can come in under 5kb for js+gz, that's your best bet here.
AFAIK optional chaining and the nullish coalescing operator are not in any browser or in Node 12. I'm am using a babel transform for it in my web projects. Also, I believe TypeScript has added support, so you get it there.