I get the appeal of TS, but why the fuck would any project tie themselves to the language in this way? Angular 2+ did it, I didn't realize Deno did as well. Very bizarre decision unless I'm missing something.
I think what you are missing is that, if you use TypeScript in Deno, the extension is .ts. What's confusing is the way Node.js+TypeScript does it, which means using TypeScript with .js extensions.
"They" dropped Angular altogether: https://blog.angular.io/finding-a-path-forward-with-angularj...