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Clarify the Suspense image loading example #8672

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Clarify the Suspense image loading example #8672

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66 changes: 31 additions & 35 deletions src/content/reference/react/Suspense.md
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Original file line number Diff line number Diff line change
Expand Up @@ -3053,21 +3053,23 @@ hr {

When a [`<ViewTransition>`](/reference/react/ViewTransition) animates a Suspense boundary's reveal, React waits for visible images to load, up to a timeout, so the animation doesn't start with a half-loaded image. This only happens during a `<ViewTransition>` update. Adding an `onLoad` handler opts a specific image out, even inside a `<ViewTransition>`.

In the example below, the Suspense boundary is wrapped in a `<ViewTransition>` and shows a profile skeleton until the portrait has loaded.

For comparison, the second button performs the same update without React. Nothing waits for the image, so the card appears immediately and the image pops in when it loads:
In this example, [`startTransition`](/reference/react/startTransition) marks both state updates as Transitions. Compare what happens when React renders the image inside and outside a `<ViewTransition>`:

<Sandpack>

```js
import { ViewTransition, Suspense, useState, startTransition } from 'react';
import {
ViewTransition,
Suspense,
useState,
startTransition,
} from 'react';
import { freshImageUrl } from './image.js';
import VanillaProfile from './VanillaProfile.js';

function Profile({ src }) {
return (
<div className="card">
<img src={src} alt="Jack Pope" width={80} height={80} />
<img src={src} alt="" width={80} height={80} />
<p>Jack Pope</p>
</div>
);
Expand All @@ -3083,47 +3085,39 @@ function ProfilePlaceholder() {
}

export default function App() {
const [src, setSrc] = useState(null);
const [viewTransitionSrc, setViewTransitionSrc] = useState(null);
const [plainSrc, setPlainSrc] = useState(null);
return (
<>
<button
onClick={() => {
startTransition(() => {
setSrc(freshImageUrl());
setViewTransitionSrc(freshImageUrl());
});
}}>
Show profile
Show profile with View Transition
</button>
{src && (
{viewTransitionSrc && (
<ViewTransition>
<Suspense fallback={<ProfilePlaceholder />}>
<Profile src={src} />
<Profile src={viewTransitionSrc} />
</Suspense>
</ViewTransition>
)}
<hr />
<VanillaProfile />
</>
);
}
```

```js src/VanillaProfile.js
import { useRef } from 'react';
import { freshImageUrl } from './image.js';

export default function VanillaProfile() {
const ref = useRef(null);
function show() {
ref.current.innerHTML = `<div class="card">
<img src="${freshImageUrl()}" alt="Jack Pope" width="80" height="80" />
<p>Jack Pope</p>
</div>`;
}
return (
<>
<button onClick={show}>Show profile (without React)</button>
<div ref={ref} />
<button
onClick={() => {
startTransition(() => {
setPlainSrc(freshImageUrl());
});
}}>
Show profile without View Transition
</button>
{plainSrc && (
<Suspense fallback={<ProfilePlaceholder />}>
<Profile src={plainSrc} />
</Suspense>
)}
</>
);
}
Expand Down Expand Up @@ -3180,6 +3174,8 @@ hr {

</Sandpack>

Inside `<ViewTransition>`, React keeps the skeleton visible while it waits for the image, up to a timeout. Outside it, React does not wait for the image before committing the card.

---

### Coordinating fonts, images, and stylesheets {/*coordinating-fonts-images-and-stylesheets*/}
Expand All @@ -3202,7 +3198,7 @@ function ProfileCard({ resources }) {
<>
<link rel="stylesheet" href={resources.stylesheet} precedence="default" />
<div className="profile-card">
<img src={resources.image} alt="Jack Pope" width={80} height={80} />
<img src={resources.image} alt="" width={80} height={80} />
<div>
<p className="name">Jack Pope</p>
<p className="bio">{quote}</p>
Expand Down Expand Up @@ -3274,7 +3270,7 @@ export default function VanillaProfileCard() {
.bio { margin: 0; font-family: 'Caveat', sans-serif; font-size: 20px; line-height: 26px; }
</style>
<div class="profile-card">
<img src="${freshImageUrl()}" alt="Jack Pope" width="80" height="80" />
<img src="${freshImageUrl()}" alt="" width="80" height="80" />
<div>
<p class="name">Jack Pope</p>
<p class="bio">${quote}</p>
Expand Down
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