Global Register type vs type-safety

[lo1tuma]

According to the documentation tanstack router requires the use of extending the existing Register interaface with the type of the custom router in order to unlock full type-safety.

I think this claim is incorrect. And it even makes things more unsafe than safe. Because it is basically a global type assertion meaning every exposed function from @tanstack/router is convinced to think the router type is always the one that has been registered. But there is no way, that the registering itself can be guaranteed to be done correctly. So if the wrong type is registered, then all the type ins components like <Link /> or in functions like useNavigation() are incorrect. This is not only an issue when registering incorrect types, but when working with multiple router instances which have different setup and thus different types. In my use-case for example I create a different router in my unit tests which only one or two example routes to test something. But according to the types of the created test routers, methods like router.navigate() indicate via their type that routes could be used that don’t exist on the test router but only on the actual app router.
I could also imagine other use-cases where someone want to have multiple router instances, for example in a monorepo where multiple different pages are deployed from (e.g. an admin-panel and a customer-facing interface).

So I think, if @tanstack/router really wants to become a fully type-safe router it needs to get rid of this approach relying on global registering of types.

[schiller-manuel]

we are always open to contributions. so please by all means share a solution for what you consider to be a problem here.

[tannerlinsley]

This feedback is so easily given without a solution. I remember having similar sentiment until I explored many alternatives which feel categorically much worse: importing the router/routeTree or its types into literally every file of your application.

There are ways around Monorepo setups, which @TkDodo is working on making public. As for the “you could make a mistake”, yes you could. But you’d quickly realize your mistake.

[danthistle-dev]

Hey @tannerlinsley! I'm currently in the process of rewriting our dashboard at work and I've opted to use TanStack Router and NX (monorepo is unavoidable). Can you give any extra info on these monorepo changes?

[TkDodo]

@beaussan has created an open-source TanStack Router monorepo setup after we had a call and went over how I’ve implemented the setup at work:

https://github.com/beaussan/tanstack-router-react-mono/tree/main

I think he will also write a blogpost on that :)

[beaussan]

Indeed, I'm working on an example project in the TanStack docs and a specific docs around monorepo and TanStack router

[lo1tuma]

You are right, I don’t really have a good solution in mind right now, that’s why I’ve opened it as a discussion instead of a feature request.

When looking at other frameworks and library, the approach how playwright handles this comes to my mind. The approach is quite simple: once you want to have a customized setup you need to call their extend() function which then returns all API methods and properties you usually import directly from playright. Those methods have to be exported from a local file which then needs to be used instead of importing playright directly.
So for tanstack this could look like this:

my-app-router.ts:

import { createRouter } from '@tanstack/router';

const { Link, useNavigate, router, /* ... */} = createRouter({ /* ... */});

export { Link, useNavigate, router, /* ... */ }

MyComponent.ts

import { useNavigate } from './my-app-router.js'

export function MyComponent(props) {
    const navigate = useNavigate();

  return <div onClick={() => navigate({ to: '/' })}>foo</div>
}

I know this is not as nice and ergonomic to use as importing those APIs directly from @tanstack/router but in terms of type-safety it would be much better.

Another approach would be to pass the router object to all APIs so the type can be inferred correctly, e.g. <Link router={myRouter} to='/'>foo</Link>.

There might be even more and better approaches than those two, that’s basically the goal of this discussion to check if someone has a good idea to make this part of @tanstack/router better without diminishing the developer experience too much.

[TkDodo]

I like both suggested approaches here theoretically, but I don’t know how they make things “better”?

Passing it directly to “Link” is a chore for every usage, which you’ll usually have hundreds of. Also, you can’t grab the router from useRouter(), because that would need to be imported, which wouldn’t have any types.

Using createRouter to create components & hooks to import from is great, until an auto-import imports from TanStack Router directly. We would need to remove those exports then - a huge breaking change. If I had to choose between the two, I would choose this option though.

So if the wrong type is registered, then all the type ins components like or in functions like useNavigation() are incorrect.

If I pass the wrong router to Link, the types will also be incorrect. If I pass the wrong router to createRouter, types will be incorrect.

Basically - if I do something wrong, it won’t work. The registry is setup once, and you can copy-paste that from the docs. I don’t see how anyone can get this wrong 🤷‍♂️

but when working with multiple router instances which have different setup and thus different types

this is indeed a problem for monorepos where you have multiple apps with different routers, as you can only module-augment once. This would be solved by the createRouter approach. I haven’t run in that case yet though.

In my use-case for example I create a different router in my unit tests which only one or two example routes to test something

We can discuss the value of such unit-tests probably at length, suffice to say I don’t believe that this is a good idea for consumers of TanStack Router because it means you write tests against a completely different route config. It will give you no confidence that your app actually works. I have also built abstractions over TanStack Router in an application and created unit tests for that, but they just test against real, existing routes. Not sure what the problem is with that ?

[lwolle]

Thanks a bunch for discussing this. We recently stumbled upon a similar situation, where we are trying to separate route trees for users and admins and thus need two routers. Surely, we could split the route trees into two apps, and just go back to one router per app, but we wanted to give this a shot, and as well, would love to not have global types.

@tannerlinsley is the router "registration" a recommendation or strictly required to make the best use of tanstack router?

• e.g. is there another way to have access to a typed Link component, if not through router registration and importing the Link?

🤘 Thanks a bunch to you and your team for supporting the community the way you do.