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The PR closes#42003.
Replace `(e: any) => void` with
`React.MouseEventHandler<HTMLAnchorElement>` and
`React.TouchEventHandler<HTMLAnchorElement>`. The original typing
overlap issue has also been fixed.
## Bug
- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`
This adapts the new client hooks of `usePathname`, `useSearchParams`,
and `useRouter` to work within the `pages/` directory to aid users
attempting to migrate shared components over to the `app/` directory.
> **Exception:**
> When the pages router is not ready, `useSearchParams` will return an
empty `URLSearchParams`. This mirrors the behavior seen in the `pages/`
directory today in that `router.query` is not available until the client
hydrates.
This also adds a new option for `useRouter` to bring it line with the
correct typings with the app directory. By default, calling
`useRouter()` will return the type `NextRouter | null` to represent what
you get when you call it from a component originating from the app
directory. If you want to instead force it to return `NextRouter` as it
does today, you can pass a boolean into the `useRouter` call as such:
```ts
const router = useRouter() // typeof router === NextRouter | null
const router = useRouter(true) // typeof router === NextRouter
```
This change is designed to ease the incremental adoption of app.
Kudos @dferber90 who found this issue. Added a test and handled it gracefully for now. Keep in mind the behavior can't be 1-1 so it takes the `as` as the `href` value given that masking of parameters in this way is no longer supported, that will be superseded by parallel routes / route interception.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
This is an initial implementation of the Server Components SWC
transformer. For the server graph, it detects client entries via the
`"client"` directive and transpile them into module reference code; for
the client graph, it removes the directives. And for both graphs, it
checks if there is any invalid imports for the given environment and
shows proper errors.
With that added, we can switch from `next-flight-client-loader` to
directly use the SWC loader in one pass. Next step is to get rid of the
`.client.` extension in other plugins.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [x] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
- Use React.startTransition instead of useTransition
- Upgrade to latest React experimental
- Split router cache invalidate into separate function
Some minor cleanup while verifying behaviors.
Follow-up to #37551
Implements prefetching for the new router.
There are multiple behaviors related to prefetching so I've split them out for each case. The list below each case is what's prefetched:
Reference:
- Checkmark checked → it's implemented.
- RSC Payload → Rendered server components.
- Router state → Patch for the router history state.
- Preloads for client component entry → This will be handled in a follow-up PR.
- No `loading.js` static case → Will be handled in a follow-up PR.
---
- `prefetch={true}` (default, same as current router, links in viewport are prefetched)
- [x] Static all the way down the component tree
- [x] RSC payload
- [x] Router state
- [ ] preloads for the client component entry
- [x] Not static all the way down the component tree
- [x] With `loading.js`
- [x] RSC payload up until the loading below the common layout
- [x] router state
- [ ] preloads for the client component entry
- [x] No `loading.js` (This case can be static files to make sure it’s fast)
- [x] router state
- [ ] preloads for the client component entry
- `prefetch={false}`
- [x] always do an optimistic navigation. We already have this implemented where it tries to figure out the router state based on the provided url. That result might be wrong but the router will automatically figure out that
---
In the first implementation there is a distinction between `hard` and `soft` navigation. With the addition of prefetching you no longer have to add a `soft` prop to `next/link` in order to leverage the `soft` case.
A heuristic has been added that automatically prefers `soft` navigation except when navigating between mismatching dynamic parameters.
An example:
- `app/[userOrTeam]/dashboard/page.js` and `app/[userOrTeam]/dashboard/settings/page.js`
- `/tim/dashboard` → `/tim/dashboard/settings` = Soft navigation
- `/tim/dashboard` → `/vercel/dashboard` = Hard navigation
- `/vercel/dashboard` → `/vercel/dashboard/settings` = Soft navigation
- `/vercel/dashboard/settings` -> `/tim/dashboard` = Hard navigation
---
While adding these new heuristics some of the tests started failing and I found some state bugs in `router.reload()` which have been fixed. An example being when you push to `/dashboard` while on `/` in the same transition it would navigate to `/`, it also wouldn't push a new history entry. Both of these cases are now fixed:
```
React.startTransition(() => {
router.push('/dashboard')
router.reload()
})
```
---
While debugging the various changes I ended up debugging and manually diffing the cache and router state quite often and was looking at a way to automate this. `useReducer` is quite similar to Redux so I was wondering if Redux Devtools could be used in order to debug the various actions as it has diffing built-in. It took a bit of time to figure out the connection mechanism but in the end I figured out how to connect `useReducer`, a new hook `useReducerWithReduxDevtools` has been added, we'll probably want to put this behind a compile-time flag when the new router is marked stable but until then it's useful to have it enabled by default (only when you have Redux Devtools installed ofcourse).
> ⚠️ Redux Devtools is only connected to take incoming actions / state. Time travel and other features are not supported because the state sent to the devtools is normalized to allow diffing the maps, you can't move backward based on that state so applying the state is not connected.
Example of the integration:
<img width="1912" alt="Screen Shot 2022-09-02 at 10 00 40" src="https://user-images.githubusercontent.com/6324199/188637303-ad8d6a81-15e5-4b65-875b-1c4f93df4e44.png">
This adds handling for prefetching `onTouchStart` as this gives a little more time to start parsing required scripts for a page transition if not already done that can help make the transition faster. This is based on research showing the touch start event firing on average `90ms` before click (x-ref: [source](https://instant.page/#:~:text=in%20the%20world.-,On%20mobile,-A%20user%20starts))
This also adds testing safari with playwright so we can run these in PRs instead of only after merge and adds initial mobile testing as well.
x-ref: [slack thread](https://vercel.slack.com/archives/C7PDM7X2M/p1658250170774989?thread_ts=1658249275.178349&cid=C7PDM7X2M)
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
* test: added some test cases for new client side router
* tests: added additional test cases
* test: improved test support
* feat: added support for `<Link soft />`
* tests: improved test reliability
* tests: added more cases for catch-all routes
* tests: added app -> pages -> app tests
* tests: add tests for useCookies + useHeaders
* tests: added tests for usePreviewData
* tests: added more tests for hooks and client components
* tests: added tests for query/params handling
* tests: fix tests for param/query to use props
* tests: added some skipped tests for unimplemented features
* tests: linting
* refactor: updated TODO -> TODO-APP
* tests: added some more test cases
* tests: skipped failing test
Renames todos to split them / make it easier to find what has to be done for the new router.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
## Client-side router for `app` directory
This PR implements the new router that leverages React 18 concurrent features like Suspense and startTransition.
It also integrates with React Server Components and builds on top of it to allow server-centric routing that only renders the part of the page that has to change.
It's one of the pieces of the implementation of https://nextjs.org/blog/layouts-rfc.
## Details
I'm going to document the differences with the current router here (will be reworked for the upgrade guide)
### Client-side cache
In the current router we have an in-memory cache for getStaticProps data so that if you prefetch and then navigate to a route that has been prefetched it'll be near-instant. For getServerSideProps the behavior is different, any navigation to a page with getServerSideProps fetches the data again.
In the new model the cache is a fundamental piece, it's more granular than at the page level and is set up to ensure consistency across concurrent renders. It can also be invalidated at any level.
#### Push/Replace (also applies to next/link)
The new router still has a `router.push` / `router.replace` method.
There are a few differences in how it works though:
- It only takes `href` as an argument, historically you had to provide `href` (the page path) and `as` (the actual url path) to do dynamic routing. In later versions of Next.js this is no longer required and in the majority of cases `as` was no longer needed. In the new router there's no way to reason about `href` vs `as` because there is no notion of "pages" in the browser.
- Both methods now use `startTransition`, you can wrap these in your own `startTransition` to get `isPending`
- The push/replace support concurrent rendering. When a render is bailed by clicking a different link to navigate to a completely different page that still works and doesn't cause race conditions.
- Support for optimistic loading states when navigating
##### Hard/Soft push/replace
Because of the client-side cache being reworked this now allows us to cover two cases: hard push and soft push.
The main difference between the two is if the cache is reused while navigating. The default for `next/link` is a `hard` push which means that the part of the cache affected by the navigation will be invalidated, e.g. if you already navigated to `/dashboard` and you `router.push('/dashboard')` again it'll get the latest version. This is similar to the existing `getServerSideProps` handling.
In case of a soft push (API to be defined but for testing added `router.softPush('/')`) it'll reuse the existing cache and not invalidate parts that are already filled in. In practice this means it's more like the `getStaticProps` client-side navigation because it does not fetch on navigation except if a part of the page is missing.
#### Back/Forward navigation
Back and Forward navigation ([popstate](https://developer.mozilla.org/en-US/docs/Web/API/Window/popstate_event)) are always handled as a soft navigation, meaning that the cache is reused, this ensures back/forward navigation is near-instant when it's in the client-side cache. This will also allow back/forward navigation to be a high priority update instead of a transition as it is based on user interaction. Note: in this PR it still uses `startTransition` as there's no way to handle the high priority update suspending which happens in case of missing data in the cache. We're working with the React team on a solution for this particular case.
### Layouts
Note: this section assumes you've read [The layouts RFC](https://nextjs.org/blog/layouts-rfc) and [React Server Components RFC](https://reactjs.org/blog/2020/12/21/data-fetching-with-react-server-components.html)
React Server Components rendering leverages the Flight streaming mechanism in React 18, this allows sending a serializable representation of the rendered React tree on the server to the browser, the client-side React can use this serialized representation to render components client-side without the JavaScript being sent to the browser. This is one of the building blocks of Server Components. This allows a bunch of interesting features but for now I'll keep it to how it affects layouts.
When you have a `app/dashboard/layout.js` and `app/dashboard/page.js` the page will render as children of the layout, when you add another page like `app/dashboard/integrations/page.js` that page falls under the dashboard layout as well. When client-side navigating the new router automatically figures out if the page you're navigating to can be a smaller render than the whole page, in this case `app/dashboard/page.js` and `app/dashboard/integrations/page.js` share the `app/dashboard/layout.js` so instead of rendering the whole page we render below the layout component, this means the layout itself does not get re-rendered, the layout's `getServerSideProps` would not be called, and the Flight response would only hold the result of `app/dashboard/integrations/page.js`, effectively giving you the smallest patch for the UI.
---
Note: the commits in this PR were mostly work in progress to ensure it wasn't lost along the way. The implementation was reworked a bunch of times to where it is now.
Co-authored-by: Jiachi Liu <4800338+huozhi@users.noreply.github.com>
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
Fixes#37981.
When handling the legacy link behavior on the current version of Next.js, it only wraps single string child in `<a>` tag. The PR fixes the issue by also wrap single number child in `<a>` tag, too.
* Extract `detect-domain-locale` to a util file
* Remove `pathNoQueryHash` in favor of `parsePath`
* Remove `hasPathPrefix` in favor of `pathHasPrefix`
* Remove `addPathPrefix` in favor of an existing util
* Bugfix parsing pathname
* Refactor `addLocale`
* Extract `removeLocale`
* Extract `basePath` utils
* Dynamic imports for `getDomainLocale`
Fixes#37248
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
Avoid anonymous function in `next/link` so DevTools show `Link` instead of `Anonymous`:
Before:
After:
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `yarn lint`
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
Adds additional tests for material-ui and stitches based on questions in the Twitter thread.
Fixes TypeScript types when `LinkProps` is imported and used in combination with `<button>`, added a TODO to change this at a later point when the new behavior is the default instead of opt-in.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `yarn lint`
Fixes https://github.com/vercel/next.js/discussions/32233⚠️ If you're looking at this PR please read the complete description including the part about incremental adoption.
## TLDR:
Official support for `<Link href="/about">About</Link>` / `<Link href="/about"><CustomComponent /></Link>` / `<Link href="/about"><strong>About</strong></Link>` where `<Link>` always renders `<a>` without edge cases where it doesn’t render `<a>`. You'll no longer have to put an empty `<a>` in `<Link>` with this enabled.
## Full context
### Changes to `<Link>`
- Added an `legacyBehavior` prop that defaults to `true` to preserve the defaults we have today, this will allow to run a codemod on existing codebases to move them to the version where `legacyBehavior` becomes `false` by default
- When using the new behavior `<Link>` always renders an `<a>` instead of having `React.cloneElement` and passing props onto a child element
- When using the new behavior props that can be passed to `<a>` can be passed to `<Link>`. Previously you could do something like `<Link href="/somewhere"><a target="_blank">Download</a></Link>` but with `<Link>` rendering `<a>` it now allows these props to be set on link. E.g. `<Link href="/somewhere" target="_blank"></Link>` / `<Link href="/somewhere" className="link"></Link>`
### Incremental Adoption / Codemod
The main reason we haven't made these changes before is that it breaks pretty much all Next.js apps, which is why I've been hesitant to make this change in the past. I've spent a bunch of time figuring out what the right approach is to rolling this out and ended up with an approach that requires existing apps to run a codemod that automatically opts their `<Link>` usage into the old behavior in order to keep the app functioning.
This codemod will auto-fix the usage where possible. For example:
- When you have `<Link href="/about"><a>About</a></Link>` it'll auto-fix to `<Link href="/about">About</Link>`
- When you have `<Link href="/about"><a onClick={() => console.log('clicked')}>About</a></Link>` it'll auto-fix to `<Link href="/about" onClick={() => console.log('clicked')}>About</Link>`
- For cases where auto-fixing can't be applied the `legacyBehavior` prop is added. When you have `<Link href="/about"><Component /></Link>` it'll transform to `<Link href="/about" legacyBehavior><Component /></Link>` so that your app keeps functioning using the old behavior for that particular link. It's then up to the dev to move that case out of the `legacyBehavior` prop.
**This default will be changed in Next.js 13, it does not affect existing apps in Next.js 12 unless opted in via `experimental.newLinkBehavior` and running the codemod.**
Some code samples of what changed:
```jsx
const CustomComponent = () => <strong>Hello</strong>
// Legacy behavior: `<a>` has to be nested otherwise it's excluded
// Renders: <a href="/about">About</a>. `<a>` has to be nested.
<Link href="/about">
<a>About</a>
</Link>
// Renders: <strong onClick={nextLinkClickHandler}>Hello</strong>. No `<a>` is included.
<Link href="/about">
<strong>Hello</strong>
</Link>
// Renders: <strong onClick={nextLinkClickHandler}>Hello</strong>. No `<a>` is included.
<Link href="/about">
<CustomComponent />
</Link>
// --------------------------------------------------
// New behavior: `<Link>` always renders `<a>`
// Renders: <a href="/about">About</a>. `<a>` no longer has to be nested.
<Link href="/about">
About
</Link>
// Renders: <a href="/about"><strong>Hello</strong></a>. `<a>` is included.
<Link href="/about">
<strong>Hello</strong>
</Link>
// Renders: <a href="/about"><strong>Hello</strong></a>. `<a>` is included.
<Link href="/about">
<CustomComponent />
</Link>
```
---
## Feature
- [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Errors have helpful link attached, see `contributing.md`
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
* fix(#35286): reset visible state when image src changed
* fix(#35286): reset visible state when link href changed
* test(image): image with new src should be re-lazyloaded
* test: apply code suggestions from @styfle's review
* test: incorrect condition of image load check
* Update next/link error when no children are provided
* update manifest
* Apply suggestions from code review
Co-authored-by: Balázs Orbán <info@balazsorban.com>
* Allow scroll prevention on hash change
Currently, `scrollToHash` is performed on every hash change, even when this change is caused by `<Link scroll={false} {...props} />`.
This change prevents scrolling in this case and allows users to specify the desired scrolling behavior in the router's `hashChangeComplete` event.
* Add test case and apply fixes
Co-authored-by: JJ Kasper <jj@jjsweb.site>
Currently, if you render `next/link` like
```ts
<Link>
<CustomComponent />
</Link>
```
and have
```tsx
interface Props {
onClick?: () => void; // <— note we're not passing event as an argument
}
function CustomComponent({ onClick }: Props) {
return <div onClick={() => onClick?.()}>Hello</div>
}
```
It'll result in error
```
link.js?f421:21 Uncaught TypeError: Cannot read property 'defaultPrevented' of undefined
```
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## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
## Bug
The `nodeName` of an anchor inside an SVG equals the lowercase `a` instead of the html anchor's uppercase `A`.
This behavior can be seen in this plain js demo: https://jsfiddle.net/L2p8f4ve/28/fixes#23252
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
## Documentation / Examples
- [ ] Make sure the linting passes
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
Fixes#22733
Regardless of whether it's recommended that Link be used with external href values or not, they can be used and `onMouseEnter` being swallowed with an external href value is unexpected behavior.
## Bug
- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [x] Make sure the linting passes by running `yarn lint`
* Bring back accidentally lost deprecation warning for using string as a children for `next/link`
* Wrap warning with the env check
* Remove warning, just go with removed comment about deprecation
- Use SWC to compile Next.js core server files
- Ensure only @babel/runtime/helpers/interopRequireDefault helper is used
Just an initial comparison to compare size difference of this change.
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes
## Bug
- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
fixes [#21606](https://github.com/vercel/next.js/issues/21606)
### Description
When using shallow routing and wanting to scroll to top by setting the `scroll` option to `true` it didn't work. This PR fixes this issue.
Makes sure a helpful error is shown for `<Link>` with multiple children
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
## Documentation / Examples
- [ ] Make sure the linting passes
# Route Announcements
## Summary
This PR improves the accessibility of NextJS's client-side navigation by announcing route changes to screen readers.
## Context
When a user who is sighted clicks on a link, they can see the content change. It's an affirmation that what the user intended to do by clicking a link actually worked! Users navigating the page via a screen-reader will not get this feedback on NextJS sites (This is an issue on many SPA-like architectures).
https://user-images.githubusercontent.com/4213649/103017382-63b02b00-44f8-11eb-9940-fb530d2d3018.mov
## Solution
Whenever there is a route change, the new `<RouteAnnouncer />` will look for a name to give the new page and then announce it! The name is found by first looking for an `h1`, falling back to `document.title`, and lastly to `pathname`. `<RouteAnnouncer />` is a visually hidden component placed within the `<AppContainer />`.
## Demo
https://user-images.githubusercontent.com/4213649/103017401-6ad73900-44f8-11eb-8050-b3e9a7e0c3f2.mov
## Inspiration
First and foremost, this PR was inspired by @marcysutton's studies and writing, [What we learned from user testing of accessible client-side routing techniques with Fable Tech Labs
](https://www.gatsbyjs.com/blog/2019-07-11-user-testing-accessible-client-routing/) as well as @madalynrose's [Accessible Routing](https://github.com/gatsbyjs/gatsby/pull/19290) PR for Gatsby.
There were also learnings gleaned from the conversations within #7681.
### Related Issues & PRs
- Resolves#7681
- Relates to #19963
Fixes#16864
The `router` can be missing in a test environment when trying to render a `Link` component. This PR bails out of `router.prefetch()` when `router` is missing.
The alternative is for users to mock `next/link` or to mock the `router` and wrap their test components.
Please let me know any feedback.
This ensures we render the locale domain on the `href` when using `next/link` previously the provided `href` was stilling being rendered which differed from the resulting `href` that was navigated to.
Fixes: https://github.com/vercel/next.js/issues/20612
This moves the scroll reset behavior to happen synchronously with the DOM commit, instead of a few ticks after the render completes.
This is necessary for components that read scroll state on mount.
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Fixes#6462
This makes sure SSG data is correctly prefetched for the default locale and other locales on the same page. Tests for this behavior have been added for catch-all and normal pages.
Closes: https://github.com/vercel/next.js/issues/19048
This pull request fixes `<Image />` not updating when new props are passed by removing external DOM mutations and relying on React to do it instead.
As an added bonus, I've extracted the intersection observer from both the `<Image />` and `<Link />` component, as their instance can be shared!
The increase in size is minor (+3B), and actually a decrease for apps using both `<Image />` and `<Link />`.
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Fixes#18698Fixes#18369
