I love JS and TS, however I really do wish they would create a new language already that doesn't have a super goofy implementation. Preferably once they figure out WebAssembly, that is.

https://lmgtfy.com/?q=regex+isogram
kek.

Ah, I see. Weird. I'll be double-checking my usage of Object.freeze in future, then.

Nice solution! The only thing I wonder about is why pairs is being created with let?

I know that in JS an object isn't really "constant", but declaring const would have prevented the individual keys from being modified.