While using the quite new tanstack router, i encountered some strange TypeScript behavior, one being the property to (from Router.navigate) being aliased to any when accessed using the Parameters<T> type built-in.

[src/main.tsx]

The second one happens at any route. I created a function with the following signature (full function here):

function artificialDelay<T>(ms = 5000): (val?: T) => Promise<T | undefined>

Using this function in the RouteOptions.beforeLoad like this:

createRootRoute({
    beforeLoad: artificialDelay(),
    component: () => (<></>),
});

Produces an gigantic error that can be summed up to the following:

Types of parameters val and opts are incompatible.

{
    search: RootSearchSchema;
    abortController: AbortController;
    preload: boolean;
    params: {};
    context: {};
    location: ParsedLocation<{}>;
    navigate: NavigateFn;
    buildLocation: BuildLocationFn<...>;
    cause: "preload" | /* 1 more */ | "stay";
}

is not assignable to type

{
    search: never;
    abortController: AbortController;
    preload: boolean;
    params: {};
    context: never;
    location: ParsedLocation<{}>;
    navigate: NavigateFn;
    buildLocation: BuildLocationFn<...>;
    cause: "preload" | /* 1 more */ | "stay";
}

Types of property search are incompatible.

Type RootSearchSchema is not assignable to type never.

You can see a minimal reproduction case here, based in the Quickstart (file-based) guide provided at the tanstack router docs page

• Router.navigate, property to being aliased to any here

• RouteOptions.beforeLoad opts.search being aliased to never here

• artificialDelay function declaration here

As much as I wanted to, this seems to be a bug in TypeScript, not a bug in the tanstack router.

I tried multiple ways to get the parameters type, with all of them resulting in any being returned.

In the function generic, it shouldn’t modify any of the parameters, returning the same type it received.