This ensures when CSS requests stall that they are included in the route load timeout so that stalled CSS requests don't block us from falling back to a hard navigation. This handles a rare case noticed by @pacocoursey where a transition did not complete while attempting to load CSS assets.
## Bug
- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
Previously, we weren't recording most (all?) of the Next.js measurements like `Next.js-hydration` in Concurrent Mode. This was mainly because the new API doesn't accept a callback.
Instead of special casing this, I've refactored it so that the measurements are just recorded when Root first flushes (via `useLayoutEffect`), which should be more or less the same timing for the old API.
Concurrent Mode is a little trickier for two reasons:
1. Flushes might be (slightly) delayed due to time-slicing and prioritization
2. Selective hydration might skew measurements in cases where full hydration is aborted
I don't have a good answer for those yet, so they'll need to be addressed when the time comes.
Just cleans up some code, doesn't change the underlying mechanism
## 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
This adds support for returning an object from `rewrites` in `next.config.js` with `beforeFiles`, `afterFiles`, and `fallback` to allow specifying rewrites at different stages of routing. The existing support for returning an array for rewrites is still supported and behaves the same way. The documentation has been updated to include information on these new stages that can be rewritten and removes the outdated note of rewrites not being able to override pages.
## 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`
- [x] Integration tests added
- [x] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
## Documentation / Examples
- [ ] Make sure the linting passes
This is a follow-up PR of #19052, where `visibility: inherit` was mistakenly added back. It was removed in #23278.
## 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
The current `<Image />` component does not fallback gracefully when JavaScript is disabled in the client / browser.
You can test this with the [official Next/Image example](https://csb-4k0kr-p8ya8f304.vercel.app/), by disabling JavaScript in the browser's DevTools. Video demo: https://streamable.com/frkvw9
This PR aims to fix this behaviour by using `<noscript></noscript>` tags to conditionally display a standard `<img>` element using the `props` passed to `<Image />` when JavaScript is disabled.
For browser sessions where JavaScript is enabled, this will not cause an increase in network requests, so there should be no downside.
One area where this PR is a bit "hacky" is that it uses a negative `margin-top` to counteract `sizerStyle.paddingTop`. From what I can tell, `sizerStyle.paddingTop` is generated on the server side, where we can not know ahead of time whether JavaScript is enabled in the browser - hence why I've opted for this solution.
Fixes#19223Fixes#21214
This PR removes the `visibility` style property change from next/image. It was previously added in #18195 to fix a bug that when no `src` is set, and that bug is not valid anymore as all images will always have `src` (and a fallback too).
It also fixes the problem that screen readers ignore elements with `visibility: hidden`.
Fixes#23201.
## Bug
- [x] Related issues #23201
- [ ] 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
Currently if you have `sizes` set in `next/image`, the image will likely be downloaded multiple times (usually twice) on Safari (macOS and iOS): the correct size for the viewport, and the original size specified in `src`.
Also make sure you have "Ignore Resource Cache" disabled in the Safari Devtools when trying to reproduce:
The root cause is the way Safari handles `<img>`'s attribute updates. Although React updates all the attributes one by one synchronously and programmatically, Safari will still try to fetch the resource immediately and won't wait for other DOM changes to be finished.
That means if we set the following 3 attributes in this order: `src`, `srcSet`, `sizes`. Safari will fetch the image when `src` is set. And then once `srcSet` is there it will fetch the resource again based on it. And finally, when `sizes` is updated it might correct the resource URL again.
So the fix here is simple: by just reordering those to `sizes`, `srcSet`, `src`, it will only load the image with the correct size only once:
<img width="1498" alt="CleanShot 2021-03-09 at 21 05 30@2x" src="https://user-images.githubusercontent.com/3676859/110477852-a27c7700-811e-11eb-88dc-d6e7895f67bd.png">
Fixes#19478.
In the current implementation, `idleTimeout` will always be thrown even if it didn't time out and `Promise.race` was resolved. This causes the error `Error: Route did not complete loading` on every route transition and Chrome Devtools will pause code execution if you have "Pause on exceptions" enabled.
This PR adds `resolvePromiseWithTimeout` which does the same thing as `Promise.race` and `idleTimeout`, but it cancels the rejection when it resolves successfully, in which case the error won't be thrown.
Fixes#21543.
Currently, the image component doesn't handle use of the `sizes` property with `layout="fill"` and `layout="responsive"` very well for small viewports. It will never include sizes smaller than the smallest viewport (640px) in the srcset, so even if you specify `sizes="30vw"` in your image, you have to download the full-viewport-width image on small devices.
This PR adds logic such that if you use `layout="fill"` and include a `sizes` property, the image component will include the full range of image sizes in the `srcset`.
It also includes an optimization where it finds the smallest `vw` value in the sizes value and combines that with the smallest viewport width, and uses that as the floor of the srcset. It does this so it doesn't unnecessarily increase transfer size by including ALL sizes. This is still a conservative optimization--for 95% of cases, taking the _largest_ `vw` size would work, but I don't see a way to do that without breaking a few corner cases.
The case of a sizes prop with `px` values is fixed but not optimized--though generally that case is less of a good fit for the fill or responsive layout anyway.
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 is a #19325 reconfigured to support a loader passed in via a `loader` prop on the Image component, rather than using a config-based approach.
The idea is that applications wanting to use a custom loader will create a wrapper element for the image component that incorporates that loader. See a simple example of this pattern in the integration tests.
This solution is similar to the one prototyped by @ricokahler in #20213 and described at https://github.com/vercel/next.js/issues/18606#issuecomment-720149156
---
Closes#19325Fixes#18606
This pull request correctly assigns boolean attributes for `<script />` to match the element as it is created by a server-side render.
Prior to this pull request, we'd double-execute `<script>` tags with the `async`, `defer`, or `nomodule` property.
---
Fixes#9070
This PR fixes a bug where we'd accidentally pass-through the user-provided `srcSet` if the image was lazy, just to then replace it when we hydrate.
---
Fixes#19041
This pull request adjusts our experimental scroll restoration behavior to use `sessionStorage` as opposed to `History#replaceState` to track scroll position.
In addition, **it eliminates a scroll event listener** and only captures when a `pushState` event happens (thereby leaving state that needs snapshotted).
These merely adjusts implementation detail, and is covered by existing tests:
```
test/integration/scroll-back-restoration/
```
---
Fixes#16690Fixes#17073Fixes#20486
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 pull request adds an `elements.delete` operation to the `useIntersection`'s cleanup function: `unobserve`.
Without this delete operation, next.js holds onto an unreachable reference of every observed element indefinitely (automatically every Link and Image is observed, so that means every rendered Link and Image element adds to the leak). I found this memory leak when building out an infinite feed in next.js with thousands of Link elements.
The final code block of the `unobserve` function body:
```tsx
// Destroy observer when there's nothing left to watch:
if (elements.size === 0) {
observer.disconnect()
observers.delete(id)
}
```
Is effectively unreachable without this delete operation, as the `elements` map will never decrease in size as it is currently. This means that there will always be at least one IntersectionObserver instance in memory if useIntersection has been used once, regardless of if there are currently any components still using the hook.
This ensures we detect domain specific locales and redirect them client-side. Tests have been added in the `i18n` suite to ensure the domain redirect is applied correctly during a client-side navigation
Fixes: https://github.com/vercel/next.js/issues/19174
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.
---
Fixes#6462
This fixes `next/image` to properly ignore inherited styles applied to the `img` tag by a parent element.
Image styling should **always** be done by a wrapper element—not to the image itself!
---
Fixes#19817Fixes#19964
This removes `import type` usage from our core files since `import type` requires a higher TypeScript version than currently expected.
Fixes: https://github.com/vercel/next.js/issues/19300
Currently if sizes is not defined, Next.js is setting sizes as:
```
(max-width: 640px) 640px, (max-width: 750px) 750px, (max-width: 828px) 828px, (max-width: 1080px) 1080px, (max-width: 1200px) 1200px, (max-width: 1920px) 1920px, (max-width: 2048px) 2048px, 3840px'
```
This pull request will make sizes be `100vw` by default, which will allow us to download "smaller" images than what's currently happening.
In a demo app I have, the difference is between downloading 488KB vs 1.4MB (in images)
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
