createHashRouter

Summary

Create a new data router that manages the application path via the URL [hash]https://developer.mozilla.org/en-US/docs/Web/API/URL/hash).

Signature

function createHashRouter(
  routes: RouteObject[],
  opts?: DOMRouterOpts,
): DataRouter

Params

routes

Application routes

opts.basename

Basename path for the application.

opts.future

Future flags to enable for the router.

opts.unstable_getContext

Function to provide the initial context values for all client side navigations/fetches

opts.hydrationData

When Server-Rendering and opting-out of automatic hydration, the hydrationData option allows you to pass in hydration data from your server-render. This will almost always be a subset of data from the StaticHandlerContext value you get back from the [StaticHandler](https://api.reactrouter.com/v7/interfaces/react_router.StaticHandler.html) query()` method:

const router = createBrowserRouter(routes, {
  hydrationData: {
    loaderData: {
      // [routeId]: serverLoaderData
    },
    // may also include `errors` and/or `actionData`
  },
});

Partial Hydration Data

You will almost always include a complete set of loaderData to hydrate a server-rendered app. But in advanced use-cases (such as Framework Mode's clientLoader), you may want to include loaderData for only some routes that were loaded/rendered on the server. This allows you to hydrate some of the routes (such as the app layout/shell) while showing a HydrateFallback and running the loaders for other routes during hydration.

A route loader will run during hydration in 2 scenarios:

No hydration data is provided
- In these cases the HydrateFallback component will render on initial hydration
The loader.hydrate property is set to true
- This allows you to run the loader even if you did not render a fallback on initial hydration (i.e., to prime a cache with hydration data)

const router = createBrowserRouter(
  [
    {
      id: "root",
      loader: rootLoader,
      Component: Root,
      children: [
        {
          id: "index",
          loader: indexLoader,
          HydrateFallback: IndexSkeleton,
          Component: Index,
        },
      ],
    },
  ],
  {
    hydrationData: {
      loaderData: {
        root: "ROOT DATA",
        // No index data provided
      },
    },
  }
);

opts.dataStrategy

Override the default data strategy of running loaders in parallel. See DataStrategyFunction.

This is a low-level API intended for advanced use-cases. This overrides React Router's internal handling of loader/action execution, and if done incorrectly will break your app code. Please use with caution and perform the appropriate testing.

By default, React Router is opinionated about how your data is loaded/submitted - and most notably, executes all of your loaders in parallel for optimal data fetching. While we think this is the right behavior for most use-cases, we realize that there is no "one size fits all" solution when it comes to data fetching for the wide landscape of application requirements.

The dataStrategy option gives you full control over how your loaders and actions are executed and lays the foundation to build in more advanced APIs such as middleware, context, and caching layers. Over time, we expect that we'll leverage this API internally to bring more first class APIs to React Router, but until then (and beyond), this is your way to add more advanced functionality for your applications data needs.

The dataStrategy function should return a key/value object of routeId -> DataStrategyResult and should include entries for any routes where a handler was executed. A DataStrategyResult indicates if the handler was successful or not based on the DataStrategyResult.type field. If the returned DataStrategyResult["result"] is a Response, React Router will unwrap it for you (via res.json or res.text). If you need to do custom decoding of a Response but want to preserve the status code, you can use the data utility to return your decoded data along with a ResponseInit.

Example dataStrategy Use Cases

Adding logging

In the simplest case, let's look at hooking into this API to add some logging for when our route loaders/actions execute:

let router = createBrowserRouter(routes, {
  async dataStrategy({ request, matches }) {
    const matchesToLoad = matches.filter((m) => m.shouldLoad);
    const results = {};
    await Promise.all(
      matchesToLoad.map(async (match) => {
        console.log(`Processing ${match.route.id}`);
        results[match.route.id] = await match.resolve();;
      })
    );
    return results;
  },
});

Middleware

Let's define a middleware on each route via handle and call middleware sequentially first, then call all loaders in parallel - providing any data made available via the middleware:

const routes = [
  {
    id: "parent",
    path: "/parent",
    loader({ request }, context) {
       // ...
    },
    handle: {
      async middleware({ request }, context) {
        context.parent = "PARENT MIDDLEWARE";
      },
    },
    children: [
      {
        id: "child",
        path: "child",
        loader({ request }, context) {
          // ...
        },
        handle: {
          async middleware({ request }, context) {
            context.child = "CHILD MIDDLEWARE";
          },
        },
      },
    ],
  },
];

let router = createBrowserRouter(routes, {
  async dataStrategy({ request, params, matches }) {
    // Run middleware sequentially and let them add data to `context`
    let context = {};
    for (const match of matches) {
      if (match.route.handle?.middleware) {
        await match.route.handle.middleware(
          { request, params },
          context
        );
      }
    }

    // Run loaders in parallel with the `context` value
    let matchesToLoad = matches.filter((m) => m.shouldLoad);
    let results = await Promise.all(
      matchesToLoad.map((match, i) =>
        match.resolve((handler) => {
          // Whatever you pass to `handler` will be passed as the 2nd parameter
          // to your loader/action
          return handler(context);
        })
      )
    );
    return results.reduce(
      (acc, result, i) =>
        Object.assign(acc, {
          [matchesToLoad[i].route.id]: result,
        }),
      {}
    );
  },
});

Custom Handler

It's also possible you don't even want to define a loader implementation at the route level. Maybe you want to just determine the routes and issue a single GraphQL request for all of your data? You can do that by setting your route.loader=true so it qualifies as "having a loader", and then store GQL fragments on route.handle:

const routes = [
  {
    id: "parent",
    path: "/parent",
    loader: true,
    handle: {
      gql: gql`
        fragment Parent on Whatever {
          parentField
        }
      `,
    },
    children: [
      {
        id: "child",
        path: "child",
        loader: true,
        handle: {
          gql: gql`
            fragment Child on Whatever {
              childField
            }
          `,
        },
      },
    ],
  },
];

let router = createBrowserRouter(routes, {
  async dataStrategy({ request, params, matches }) {
    // Compose route fragments into a single GQL payload
    let gql = getFragmentsFromRouteHandles(matches);
    let data = await fetchGql(gql);
    // Parse results back out into individual route level `DataStrategyResult`'s
    // keyed by `routeId`
    let results = parseResultsFromGql(data);
    return results;
  },
});

opts.patchRoutesOnNavigation

Lazily define portions of the route tree on navigations. See PatchRoutesOnNavigationFunction.

By default, React Router wants you to provide a full route tree up front via createBrowserRouter(routes). This allows React Router to perform synchronous route matching, execute loaders, and then render route components in the most optimistic manner without introducing waterfalls. The tradeoff is that your initial JS bundle is larger by definition - which may slow down application start-up times as your application grows.

To combat this, we introduced [route.lazy][route-lazy] in [v6.9.0][6-9-0] which let's you lazily load the route implementation (loader, Component, etc.) while still providing the route definition aspects up front (path, index, etc.). This is a good middle ground because React Router still knows about your route definitions (the lightweight part) up front and can perform synchronous route matching, but then delay loading any of the route implementation aspects (the heavier part) until the route is actually navigated to.

In some cases, even this doesn't go far enough. For very large applications, providing all route definitions up front can be prohibitively expensive. Additionally, it might not even be possible to provide all route definitions up front in certain Micro-Frontend or Module-Federation architectures.

This is where patchRoutesOnNavigation comes in ([RFC][fog-of-war-rfc]). This API is for advanced use-cases where you are unable to provide the full route tree up-front and need a way to lazily "discover" portions of the route tree at runtime. This feature is often referred to as ["Fog of War"][fog-of-war] because similar to how video games expand the "world" as you move around - the router would be expanding its routing tree as the user navigated around the app - but would only ever end up loading portions of the tree that the user visited.

patchRoutesOnNavigation will be called anytime React Router is unable to match a path. The arguments include the path, any partial matches, and a patch function you can call to patch new routes into the tree at a specific location. This method is executed during the loading portion of the navigation for GET requests and during the submitting portion of the navigation for non-GET requests.

Example patchRoutesOnNavigation Use Cases

Patching children into an existing route

const router = createBrowserRouter(
  [
    {
      id: "root",
      path: "/",
      Component: RootComponent,
    },
  ],
  {
    async patchRoutesOnNavigation({ path, patch }) {
      if (path === "/a") {
        // Load/patch the `a` route as a child of the route with id `root`
        let route = await getARoute();
        //  ^ { path: 'a', Component: A }
        patch("root", [route]);
      }
    },
  }
);

In the above example, if the user clicks a link to /a, React Router won't match any routes initially and will call patchRoutesOnNavigation with a path = "/a" and a matches array containing the root route match. By calling patch('root', [route]), the new route will be added to the route tree as a child of the root route and React Router will perform matching on the updated routes. This time it will successfully match the /a path and the navigation will complete successfully.

Patching new root-level routes

If you need to patch a new route to the top of the tree (i.e., it doesn't have a parent), you can pass null as the routeId:

const router = createBrowserRouter(
  [
    {
      id: "root",
      path: "/",
      Component: RootComponent,
    },
  ],
  {
    async patchRoutesOnNavigation({ path, patch }) {
      if (path === "/root-sibling") {
        // Load/patch the `/root-sibling` route as a sibling of the root route
        let route = await getRootSiblingRoute();
        //  ^ { path: '/root-sibling', Component: RootSibling }
        patch(null, [route]);
      }
    },
  }
);

Patching sub-trees asynchronously

You can also perform asynchronous matching to lazily fetch entire sections of your application:

let router = createBrowserRouter(
  [
    {
      path: "/",
      Component: Home,
    },
  ],
  {
    async patchRoutesOnNavigation({ path, patch }) {
      if (path.startsWith("/dashboard")) {
        let children = await import("./dashboard");
        patch(null, children);
      }
      if (path.startsWith("/account")) {
        let children = await import("./account");
        patch(null, children);
      }
    },
  }
);

If in-progress execution of patchRoutesOnNavigation is interrupted by a subsequent navigation, then any remaining patch calls in the interrupted execution will not update the route tree because the operation was cancelled.

Co-locating route discovery with route definition

If you don't wish to perform your own pseudo-matching, you can leverage the partial matches array and the handle field on a route to keep the children definitions co-located:

let router = createBrowserRouter(
  [
    {
      path: "/",
      Component: Home,
    },
    {
      path: "/dashboard",
      children: [
        {
          // If we want to include /dashboard in the critical routes, we need to
          // also include it's index route since patchRoutesOnNavigation will not be
          // called on a navigation to `/dashboard` because it will have successfully
          // matched the `/dashboard` parent route
          index: true,
          // ...
        },
      ],
      handle: {
        lazyChildren: () => import("./dashboard"),
      },
    },
    {
      path: "/account",
      children: [
        {
          index: true,
          // ...
        },
      ],
      handle: {
        lazyChildren: () => import("./account"),
      },
    },
  ],
  {
    async patchRoutesOnNavigation({ matches, patch }) {
      let leafRoute = matches[matches.length - 1]?.route;
      if (leafRoute?.handle?.lazyChildren) {
        let children =
          await leafRoute.handle.lazyChildren();
        patch(leafRoute.id, children);
      }
    },
  }
);

A note on routes with parameters

Because React Router uses ranked routes to find the best match for a given path, there is an interesting ambiguity introduced when only a partial route tree is known at any given point in time. If we match a fully static route such as path: "/about/contact-us" then we know we've found the right match since it's composed entirely of static URL segments, and thus we do not need to bother asking for any other potentially higher-scoring routes.

However, routes with parameters (dynamic or splat) can't make this assumption because there might be a not-yet-discovered route tht scores higher. Consider a full route tree such as:

// Assume this is the full route tree for your app
const routes = [
  {
    path: "/",
    Component: Home,
  },
  {
    id: "blog",
    path: "/blog",
    Component: BlogLayout,
    children: [
      { path: "new", Component: NewPost },
      { path: ":slug", Component: BlogPost },
    ],
  },
];

And then assume we want to use patchRoutesOnNavigation to fill this in as the user navigates around:

// Start with only the index route
const router = createBrowserRouter(
  [
    {
      path: "/",
      Component: Home,
    },
  ],
  {
    patchRoutesOnNavigation({ path, patch }) {
      if (path === "/blog/new") {
        patch("blog", [
          {
            path: "new",
            Component: NewPost,
          },
        ]);
      } else if (path.startsWith("/blog")) {
        patch("blog", [
          {
            path: ":slug",
            Component: BlogPost,
          },
        ]);
      }
    },
  }
);

If the user were to a blog post first (i.e., /blog/my-post) we would patch in the :slug route. Then if the user navigated to /blog/new to write a new post, we'd match /blog/:slug but it wouldn't be the right match! We need to call patchRoutesOnNavigation just in case there exists a higher-scoring route we've not yet discovered, which in this case there is.

So, anytime React Router matches a path that contains at least one param, it will call patchRoutesOnNavigation and match routes again just to confirm it has found the best match.

If your patchRoutesOnNavigation implementation is expensive or making side-effect fetch calls to a backend server, you may want to consider tracking previously seen routes to avoid over-fetching in cases where you know the proper route has already been found. This can usually be as simple as maintaining a small cache of prior path values for which you've already patched in the right routes:

let discoveredRoutes = new Set();

const router = createBrowserRouter(routes, {
  patchRoutesOnNavigation({ path, patch }) {
    if (discoveredRoutes.has(path)) {
      // We've seen this before so nothing to patch in and we can let the router
      // use the routes it already knows about
      return;
    }

    discoveredRoutes.add(path);

    // ... patch routes in accordingly
  },
});

opts.window

Window object override - defaults to the global window instance.

Returns

An initialized data router to pass to <RouterProvider>