Add unstable_flushSync option

.changeset/flush-sync-router.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/router": minor
+---
+
+Add `unstable_flushSync` option to `router.navigate` and `router.fetch` to tell the React Router layer to opt-out of `React.startTransition` and into `ReactDOM.flushSync` for state updates

.changeset/flush-sync.md

@@ -0,0 +1,6 @@
+---
+"react-router-dom": minor
+"react-router": minor
+---
+
+Add `unstable_flushSync` option to `useNavigate`/`useSumbit`/`fetcher.load`/`fetcher.submit` to opt-out of `React.startTransition` and into `ReactDOM.flushSync` for state updates

docs/hooks/use-fetcher.md

@@ -107,7 +107,7 @@ function SomeComponent() {
 
 ## Methods
 
-## `fetcher.load()`
+### `fetcher.load(href, options)`
 
 Loads data from a route loader.
 
@@ -133,7 +133,15 @@ If you find yourself calling this function inside of click handlers, you can pro
 
 <docs-info>Any `fetcher.load` calls that are active on the page will be re-executed as part of revalidation (either after a navigation submission, another fetcher submission, or a `useRevalidator()` call)</docs-info>
 
-## `fetcher.submit()`
+#### `options.unstable_flushSync`
+
+The `unstable_flushSync` option tells React Router DOM to wrap the initial state update for this `fetcher.load` in a [`ReactDOM.flushSync`][flush-sync] call instead of the default [`React.startTransition`][start-transition]. This allows you to perform synchronous DOM actions immediately after the update is flushed to the DOM.
+
+<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
+
+<docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
+
+### `fetcher.submit()`
 
 The imperative version of `<fetcher.Form>`. If a user interaction should initiate the fetch, you should use `<fetcher.Form>`. But if you, the programmer are initiating the fetch (not in response to a user clicking a button, etc.), then use this function.
 
@@ -279,3 +287,5 @@ fetcher.formMethod; // "post"
 [api-development-strategy]: ../guides/api-development-strategy
 [use-submit]: ./use-submit
 [use-fetchers]: ./use-fetchers
+[flush-sync]: https://react.dev/reference/react-dom/flushSync
+[start-transition]: https://react.dev/reference/react/startTransition

docs/hooks/use-navigate.md

@@ -20,6 +20,8 @@ interface NavigateOptions {
   state?: any;
   preventScrollReset?: boolean;
   relative?: RelativeRoutingType;
+  unstable_flushSync?: boolean;
+  unstable_viewTransition?: boolean;
 }
 
 type RelativeRoutingType = "route" | "path";
@@ -85,6 +87,16 @@ function EditContact() {
 }
 ```
 
+## `options.unstable_flushSync`
+
+The `unstable_flushSync` option tells React Router DOM to wrap the initial state update for this navigation in a [`ReactDOM.flushSync`][flush-sync] call instead of the default [`React.startTransition`][start-transition]. This allows you to perform synchronous DOM actions immediately after the update is flushed to the DOM.
+
+<docs-warning>`unstable_flushSync` only works when using a data router, see [Picking a Router][picking-a-router]</docs-warning>
+
+<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
+
+<docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
+
 ## `options.unstable_viewTransition`
 
 The `unstable_viewTransition` option enables a [View Transition][view-transitions] for this navigation by wrapping the final state update in `document.startViewTransition()`. If you need to apply specific styles for this view transition, you will also need to leverage the [`unstable_useViewTransitionState()`][use-view-transition-state].
@@ -102,3 +114,5 @@ The `unstable_viewTransition` option enables a [View Transition][view-transition
 [use-view-transition-state]: ../hooks//use-view-transition-state
 [view-transitions]: https://developer.mozilla.org/en-US/docs/Web/API/View_Transitions_API
 [picking-a-router]: ../routers/picking-a-router
+[flush-sync]: https://react.dev/reference/react-dom/flushSync
+[start-transition]: https://react.dev/reference/react/startTransition

docs/hooks/use-submit.md

@@ -160,5 +160,15 @@ Because submissions are navigations, the options may also contain the other navi
 - `state`
 - `unstable_viewTransition`
 
+### `options.unstable_flushSync`
+
+The `unstable_flushSync` option tells React Router DOM to wrap the initial state update for this submission in a [`ReactDOM.flushSync`][flush-sync] call instead of the default [`React.startTransition`][start-transition]. This allows you to perform synchronous DOM actions immediately after the update is flushed to the DOM.
+
+<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
+
+<docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
+
 [pickingarouter]: ../routers/picking-a-router
 [form]: ../components/form
+[flush-sync]: https://react.dev/reference/react-dom/flushSync
+[start-transition]: https://react.dev/reference/react/startTransition

package.json

@@ -110,7 +110,7 @@
   },
   "filesize": {
     "packages/router/dist/router.umd.min.js": {
-      "none": "49.0 kB"
+      "none": "49.2 kB"
     },
     "packages/react-router/dist/react-router.production.min.js": {
       "none": "13.9 kB"
@@ -119,10 +119,10 @@
       "none": "16.3 kB"
     },
     "packages/react-router-dom/dist/react-router-dom.production.min.js": {
-      "none": "16.1 kB"
+      "none": "16.7 kB"
     },
     "packages/react-router-dom/dist/umd/react-router-dom.production.min.js": {
-      "none": "22.3 kB"
+      "none": "22.9 kB"
     }
   }
 }