The ts-regexp package `infer`s out of template literal types to do its magic. That's possible from JSDoc too: https://www.typescriptlang.org/play/?filetype=js#code/PQKhCg...

The behavior of ts-regexp is not especially related to the `RegExpExecArray` type. That package uses unsafe assertions to implement its API.

The only thing that requires TypeScript syntax in the playground you linked is the non-null assertions. Here's that same code in JSDoc mode with the non-null assertions removed (`strictNullChecks` is disabled instead): https://www.typescriptlang.org/play/?filetype=js#code/JYWwDg...

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> For my use-case, I just want to know that I can change either my code or regex and I'll be alerted before runtime or buildtime if I've forgotten to account for something.

If you can show a concrete example what you want using TypeScript syntax then I'm pretty sure I could port it to JSDoc syntax. (To be clear I'd personally much rather write the TypeScript syntax as I find JSDoc comments annoying & verbose, but they're plenty powerful, being nearly isomorphic to TypeScript annotations.)