Add full TypeScript support & inference

[tgriesser]

👋 pretty big PR, and a breaking change from the current type definition structure (though no runtime-api changes), so I'll give a summary of the things that make it a worthwhile addition 😄

Auto-inference of parameters & method in a route:

Uses TypeScript's generic capturing + advanced conditionals & mapped properties, in combination with the newer (4.1+) feature of "Template Literal Types" to Infer the route params in the handler (closes #116):

Also handles trailing optional params correctly:

Types the method name as the string constant literal (GET, POST, ...), rather than string when it's one of the "known" methods

Properly allows typing the "rest" args to a handler call:

Without providing generics, we default to [unknown, ExecutionContext]:

With generics, we can get the Env:

Explicit TS extension via additional Router() generic property:

Additional changes & info:

• IttyRequest interface is intersected with the current global Request interface, leading to better inference & less needing to cast types in method handlers (closes #105)
• Adds query: Record<string, string>; typing for the IttyRequest interface
• Adds typechecks.ts as the place to add assertions (both positive and negative via // @ts-expect-error) for different use-cases
• Tries to keep the build system simple

[tgriesser]

Actually just noticed that this library isn't meant to be used exclusively w/ Cloudflare. Let me know if that's still a design goal, and I can try to rework the types a bit.

[kwhitley]

Actually just noticed that this library isn't meant to be used exclusively w/ Cloudflare. Let me know if that's still a design goal, and I can try to rework the types a bit.

Appreciate all the work on this, but you're absolutely correct... it's meant to take a generic request-like object (any object with method + url properties) and route accordingly... while it was designed for my own use with Cloudflare, I absolutely wanted to leave the core lib as generic/vague as possible to allow various downstream solutions.

[tgriesser]

while it was designed for my own use with Cloudflare, I absolutely wanted to leave the core lib as generic/vague as possible to allow various downstream solutions.

Cool, in that case, I stripped the /// <reference types="@cloudflare/workers-types" /> and updated it to make the types a bit more flexible/correct, adding some type-tests to ensure things work with the correct inferred types both in a Cloudflare & generic runtime. I can update the docs a bit if you think this is something you might be interested in landing.

Also if you don't want to overcomplicate things with all the extra type noise, I'd totally respect that and be fine publishing as a different lib. Getting the types right in the library leads to less casting & pain everywhere else, but means there's quite a lot going on to keep things both flexible & correct.

[tgriesser]

Alternatively, I could just extract the new types and replace those in the current itty-router.d.ts, and keep the JS implementation as-is

[tgriesser]

Closing in favor of #119