[["$r","MaxWidth","58",{"children":[["$r","p",null,{"children":["April 23, 2025 by ",["$r","a",null,{"href":"https://twitter.com/rickhanlonii","target":"_blank","rel":"nofollow noopener noreferrer","children":"Ricky Hanlon"}]]}],"\n",["$r","hr",null,{}],"\n",["$r","Intro",null,{"children":["$r","p",null,{"children":"In React Labs posts, we write about projects in active research and development. In this post, we’re sharing two new experimental features that are ready to try today, and updates on other areas we’re working on now."}]}],"\n",["$r","p",null,{"children":"Today, we’re excited to release documentation for two new experimental features that are ready for testing:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":["$r","a",null,{"href":"#view-transitions","children":"View Transitions"}]}],"\n",["$r","li",null,{"children":["$r","a",null,{"href":"#activity","children":"Activity"}]}],"\n"]}],"\n",["$r","p",null,{"children":"We’re also sharing updates on new features currently in development:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":["$r","a",null,{"href":"#react-performance-tracks","children":"React Performance Tracks"}]}],"\n",["$r","li",null,{"children":["$r","a",null,{"href":"#compiler-ide-extension","children":"Compiler IDE Extension"}]}],"\n",["$r","li",null,{"children":["$r","a",null,{"href":"#automatic-effect-dependencies","children":"Automatic Effect Dependencies"}]}],"\n",["$r","li",null,{"children":["$r","a",null,{"href":"#fragment-refs","children":"Fragment Refs"}]}],"\n",["$r","li",null,{"children":["$r","a",null,{"href":"#concurrent-stores","children":"Concurrent Stores"}]}],"\n"]}],"\n",["$r","hr",null,{}],"\n",["$r","h1",null,{"id":"new-experimental-features","children":"New Experimental Features "}],"\n",["$r","Note",null,{"children":[["$r","p",null,{"children":[["$r","code",null,{"children":""}]," has shipped in ",["$r","code",null,{"children":"react@19.2"}],"."]}],["$r","p",null,{"children":[["$r","code",null,{"children":""}]," and ",["$r","code",null,{"children":"addTransitionType"}]," are now available in ",["$r","code",null,{"children":"react@canary"}],"."]}]]}],"\n",["$r","p",null,{"children":["View Transitions and Activity are now ready for testing in ",["$r","code",null,{"children":"react@experimental"}],". These features have been tested in production and are stable, but the final API may still change as we incorporate feedback."]}],"\n",["$r","p",null,{"children":"You can try them by upgrading React packages to the most recent experimental version:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":["$r","code",null,{"children":"react@experimental"}]}],"\n",["$r","li",null,{"children":["$r","code",null,{"children":"react-dom@experimental"}]}],"\n"]}],"\n",["$r","p",null,{"children":"Read on to learn how to use these features in your app, or check out the newly published docs:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":[["$r","a",null,{"href":"/reference/react/ViewTransition","children":["$r","code",null,{"children":""}]}],": A component that lets you activate an animation for a Transition."]}],"\n",["$r","li",null,{"children":[["$r","a",null,{"href":"/reference/react/addTransitionType","children":["$r","code",null,{"children":"addTransitionType"}]}],": A function that allows you to specify the cause of a Transition."]}],"\n",["$r","li",null,{"children":[["$r","a",null,{"href":"/reference/react/Activity","children":["$r","code",null,{"children":""}]}],": A component that lets you hide and show parts of the UI."]}],"\n"]}],"\n",["$r","h2",null,{"id":"view-transitions","children":"View Transitions "}],"\n",["$r","p",null,{"children":["React View Transitions are a new experimental feature that makes it easier to add animations to UI transitions in your app. Under-the-hood, these animations use the new ",["$r","a",null,{"href":"https://developer.mozilla.org/en-US/docs/Web/API/Document/startViewTransition","target":"_blank","rel":"nofollow noopener noreferrer","children":["$r","code",null,{"children":"startViewTransition"}]}]," API available in most modern browsers."]}],"\n",["$r","p",null,{"children":["To opt-in to animating an element, wrap it in the new ",["$r","code",null,{"children":""}]," component:"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","children":"// \"what\" to animate.\n\n

animate me

\n\n"}]}],"\n",["$r","p",null,{"children":"This new component lets you declaratively define “what” to animate when an animation is activated."}],"\n",["$r","p",null,{"children":"You can define “when” to animate by using one of these three triggers for a View Transition:"}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","children":"// \"when\" to animate.\n\n// Transitions\nstartTransition(() => setState(...));\n\n// Deferred Values\nconst deferred = useDeferredValue(value);\n\n// Suspense\n}>\n

\n\n"}]}],"\n",["$r","p",null,{"children":["By default, these animations use the ",["$r","a",null,{"href":"https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#customizing_your_animations","target":"_blank","rel":"nofollow noopener noreferrer","children":"default CSS animations for View Transitions"}]," applied (typically a smooth cross-fade). You can use ",["$r","a",null,{"href":"https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#the_view_transition_pseudo-element_tree","target":"_blank","rel":"nofollow noopener noreferrer","children":"view transition pseudo-selectors"}]," to define “how” the animation runs. For example, you can use ",["$r","code",null,{"children":"*"}]," to change the default animation for all transitions:"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"children":"// \"how\" to animate.\n::view-transition-old(*) {\n animation: 300ms ease-out fade-out;\n}\n::view-transition-new(*) {\n animation: 300ms ease-in fade-in;\n}\n"}]}],"\n",["$r","p",null,{"children":["When the DOM updates due to an animation trigger—like ",["$r","code",null,{"children":"startTransition"}],", ",["$r","code",null,{"children":"useDeferredValue"}],", or a ",["$r","code",null,{"children":"Suspense"}]," fallback switching to content—React will use ",["$r","a",null,{"href":"/reference/react/ViewTransition#viewtransition","children":"declarative heuristics"}]," to automatically determine which ",["$r","code",null,{"children":""}]," components to activate for the animation. The browser will then run the animation that’s defined in CSS."]}],"\n",["$r","p",null,{"children":["If you’re familiar with the browser’s View Transition API and want to know how React supports it, check out ",["$r","a",null,{"href":"/reference/react/ViewTransition#how-does-viewtransition-work","children":["How does ",["$r","code",null,{"children":""}]," Work"]}]," in the docs."]}],"\n",["$r","p",null,{"children":"In this post, let’s take a look at a few examples of how to use View Transitions."}],"\n",["$r","p",null,{"children":"We’ll start with this app, which doesn’t animate any of the following interactions:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":"Click a video to view the details."}],"\n",["$r","li",null,{"children":"Click “back” to go back to the feed."}],"\n",["$r","li",null,{"children":"Type in the list to filter the videos."}],"\n"]}],"\n"]}],["$r","Sandpack",null,{"children":[["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/App.js active","children":"import TalkDetails from './Details'; import Home from './Home'; import {useRouter} from './router';\n\nexport default function App() {\n const {url} = useRouter();\n\n // 🚩This version doesn't include any animations yet\n return url === '/' ? : ;\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js","children":"import { fetchVideo, fetchVideoDetails } from \"./data\";\nimport { Thumbnail, VideoControls } from \"./Videos\";\nimport { useRouter } from \"./router\";\nimport Layout from \"./Layout\";\nimport { use, Suspense } from \"react\";\nimport { ChevronLeft } from \"./Icons\";\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n );\n}\n\nexport default function Details() {\n const { url, navigateBack } = useRouter();\n const videoId = url.split(\"/\").pop();\n const video = use(fetchVideo(videoId));\n\n return (\n {\n navigateBack(\"/\");\n }}\n >\n Back\n \n }\n >\n

\n \n \n \n }>\n \n \n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js","children":"import { Video } from \"./Videos\";\nimport Layout from \"./Layout\";\nimport { fetchVideos } from \"./data\";\nimport { useId, useState, use } from \"react\";\nimport { IconSearch } from \"./Icons\";\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState(\"\");\n const foundVideos = filterVideos(videos, searchText);\n return (\n {count} Videos}>\n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js","children":"import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {heading}\n {isPending && }\n

\n\n

{children}

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js","children":"import { useState } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Thumbnail({ video, children }) {\n return (\n \n {children}\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

}\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js hidden","children":"import { fetchVideo, fetchVideoDetails } from \"./data\";\nimport { Thumbnail, VideoControls } from \"./Videos\";\nimport { useRouter } from \"./router\";\nimport Layout from \"./Layout\";\nimport { use, Suspense } from \"react\";\nimport { ChevronLeft } from \"./Icons\";\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n }>\n \n \n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js hidden","children":"import { Video } from \"./Videos\";\nimport Layout from \"./Layout\";\nimport { fetchVideos } from \"./data\";\nimport { useId, useState, use } from \"react\";\nimport { IconSearch } from \"./Icons\";\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState(\"\");\n const foundVideos = filterVideos(videos, searchText);\n return (\n {count} Videos}>\n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n\n return (\n

\n {heading}\n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Thumbnail({ video, children }) {\n return (\n \n {children}\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

{details.title}

{details.description}

\n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n }>\n \n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n\n return (\n

\n {heading}\n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

{details.title}

{details.description}

\n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n }>\n \n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n\n return (\n

\n {heading}\n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js active","children":"import { useState, ViewTransition } from \"react\"; import LikeButton from \"./LikeButton\"; import { useRouter } from \"./router\"; import { PauseIcon, PlayIcon } from \"./Icons\"; import { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

{details.title}

{details.description}

\n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n }>\n \n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js active","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

}\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js active","children":"import { use, Suspense, ViewTransition } from \"react\"; import { fetchVideo, fetchVideoDetails } from \"./data\"; import { Thumbnail, VideoControls } from \"./Videos\"; import { useRouter } from \"./router\"; import Layout from \"./Layout\"; import { ChevronLeft } from \"./Icons\";\n\nfunction VideoDetails({ id }) {\n // Cross-fade the fallback to content.\n return (\n \n }>\n \n \n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n

\n );\n}\n\nexport default function Details() {\n const { url, navigateBack } = useRouter();\n const videoId = url.split(\"/\").pop();\n const video = use(fetchVideo(videoId));\n\n return (\n {\n navigateBack(\"/\");\n }}\n >\n Back\n \n }\n >\n

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n

{details.title}

{details.description}

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js hidden","children":"import { Video } from \"./Videos\";\nimport Layout from \"./Layout\";\nimport { fetchVideos } from \"./data\";\nimport { useId, useState, use } from \"react\";\nimport { IconSearch } from \"./Icons\";\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState(\"\");\n const foundVideos = filterVideos(videos, searchText);\n return (\n {count} Videos}>\n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react';\nimport { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

}\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js active","children":"import { use, Suspense, ViewTransition } from \"react\"; import { fetchVideo, fetchVideoDetails } from \"./data\"; import { Thumbnail, VideoControls } from \"./Videos\"; import { useRouter } from \"./router\"; import Layout from \"./Layout\"; import { ChevronLeft } from \"./Icons\";\n\nfunction VideoDetails({ id }) {\n return (\n \n \n \n }\n >\n {/* Animate the content up */}\n \n \n \n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js hidden","children":"import { Video } from \"./Videos\";\nimport Layout from \"./Layout\";\nimport { fetchVideos } from \"./data\";\nimport { useId, useState, use } from \"react\";\nimport { IconSearch } from \"./Icons\";\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState(\"\");\n const foundVideos = filterVideos(videos, searchText);\n return (\n {count} Videos}>\n \n

\n {foundVideos.length === 0 && (\n

No results

\n )}\n

\n {foundVideos.map((video) => (\n

\n \n );\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react';\nimport { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

\n {filteredVideos.map((video) => (\n \n

\n ))}\n

\n"}]}],"\n",["$r","p",null,{"children":["To activate the ViewTransition, we can use ",["$r","code",null,{"children":"useDeferredValue"}],":"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"{2}","children":"const [searchText, setSearchText] = useState('');\nconst deferredSearchText = useDeferredValue(searchText);\nconst filteredVideos = filterVideos(videos, deferredSearchText);\n"}]}],"\n",["$r","p",null,{"children":"Now the items animate as you type in the search bar:"}],"\n"]}],["$r","Sandpack",null,{"children":[["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/App.js hidden","children":"import { ViewTransition } from \"react\";\nimport Details from \"./Details\";\nimport Home from \"./Home\";\nimport { useRouter } from \"./router\";\n\nexport default function App() {\n const { url } = useRouter();\n\n // Default slow-fade animation.\n return (\n \n {url === \"/\" ? :

}\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js hidden","children":"import { use, Suspense, ViewTransition } from \"react\";\nimport { fetchVideo, fetchVideoDetails } from \"./data\";\nimport { Thumbnail, VideoControls } from \"./Videos\";\nimport { useRouter } from \"./router\";\nimport Layout from \"./Layout\";\nimport { ChevronLeft } from \"./Icons\";\n\nfunction VideoDetails({id}) {\n // Animate from Suspense fallback to content\n return (\n \n \n \n }\n >\n {/* Animate the content up */}\n \n \n \n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js","children":"import { useId, useState, use, useDeferredValue, ViewTransition } from \"react\";import { Video } from \"./Videos\";import Layout from \"./Layout\";import { fetchVideos } from \"./data\";import { IconSearch } from \"./Icons\";\n\nfunction SearchList({searchText, videos}) {\n // Activate with useDeferredValue (\"when\")\n const deferredSearchText = useDeferredValue(searchText);\n const filteredVideos = filterVideos(videos, deferredSearchText);\n return (\n

\n {filteredVideos.map((video) => (\n // Animate each item in list (\"what\")\n \n

\n ))}\n

\n {filteredVideos.length === 0 && (\n

No results

\n )}\n

\n );\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState('');\n\n return (\n {count} Videos}>\n \n \n \n );\n}\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react';\nimport { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

}\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js","children":"import { use, Suspense, ViewTransition } from \"react\"; import { fetchVideo, fetchVideoDetails } from \"./data\"; import { Thumbnail, VideoControls } from \"./Videos\"; import { useRouter } from \"./router\"; import Layout from \"./Layout\"; import { ChevronLeft } from \"./Icons\";\n\nfunction VideoDetails({id}) {\n // Animate from Suspense fallback to content\n return (\n \n \n \n }\n >\n {/* Animate the content up */}\n \n \n \n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n {filteredVideos.map((video) => (\n // Animate each item in list (\"what\")\n \n

\n ))}\n

\n {filteredVideos.length === 0 && (\n

No results

\n )}\n

\n );\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState('');\n\n return (\n {count} Videos}>\n \n \n \n );\n}\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js","children":"import { useState, ViewTransition } from \"react\"; import LikeButton from \"./LikeButton\"; import { useRouter } from \"./router\"; import { PauseIcon, PlayIcon } from \"./Icons\"; import { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n return (\n \n \n {children}\n \n \n );\n}\n\n\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

}\n \n );\n}\n"}]}],"\n",["$r","p",null,{"children":["However, this means if the user goes back to the old page, all of the previous state is lost. For example, if the ",["$r","code",null,{"children":""}]," page has an ",["$r","code",null,{"children":""}]," field, when the user leaves the page the ",["$r","code",null,{"children":""}]," is unmounted, and all of the text they had typed is lost."]}],"\n",["$r","p",null,{"children":["Activity allows you to keep the state around as the user changes pages, so when they come back they can resume where they left off. This is done by wrapping part of the tree in ",["$r","code",null,{"children":""}]," and toggling the ",["$r","code",null,{"children":"mode"}],":"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"{6-8}","children":"function App() {\n const { url } = useRouter();\n\n return (\n <>\n \n \n \n {url !== '/' &&

}\n \n );\n}\n"}]}],"\n",["$r","p",null,{"children":"With this change, we can improve on our View Transitions example above. Before, when you searched for a video, selected one, and returned, your search filter was lost. With Activity, your search filter is restored and you can pick up where you left off."}],"\n",["$r","p",null,{"children":"Try searching for a video, selecting it, and clicking “back”:"}],"\n"]}],["$r","Sandpack",null,{"children":[["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/App.js","children":"import { Activity, ViewTransition } from \"react\"; import Details from \"./Details\"; import Home from \"./Home\"; import { useRouter } from \"./router\";\n\nexport default function App() {\n const { url } = useRouter();\n\n return (\n // View Transitions know about Activity\n \n {/* Render Home in Activity so we don't lose state */}\n \n \n \n {url !== '/' &&

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Home.js hidden","children":"import { useId, useState, use, useDeferredValue, ViewTransition } from \"react\";import { Video } from \"./Videos\";import Layout from \"./Layout\";import { fetchVideos } from \"./data\";import { IconSearch } from \"./Icons\";\n\nfunction SearchList({searchText, videos}) {\n // Activate with useDeferredValue (\"when\")\n const deferredSearchText = useDeferredValue(searchText);\n const filteredVideos = filterVideos(videos, deferredSearchText);\n return (\n

\n {filteredVideos.length === 0 && (\n

No results

\n )}\n

\n {filteredVideos.map((video) => (\n // Animate each item in list (\"what\")\n \n

\n ))}\n

\n );\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState('');\n\n return (\n {count} Videos}>\n \n \n \n );\n}\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

\n \n \n

\n \n\n"}]}],"\n",["$r","p",null,{"children":"With this update, if the content on the next page has time to pre-render, it will animate in without the Suspense fallback. Click a video, and notice that the video title and description on the Details page render immediately, without a fallback:"}],"\n"]}],["$r","Sandpack",null,{"children":[["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/App.js","children":"import { Activity, ViewTransition, use } from \"react\"; import Details from \"./Details\"; import Home from \"./Home\"; import { useRouter } from \"./router\"; import {fetchVideos} from './data';\n\nexport default function App() {\n const { url } = useRouter();\n const videoId = url.split(\"/\").pop();\n const videos = use(fetchVideos());\n\n return (\n \n {/* Render videos in Activity to pre-render them */}\n {videos.map(({id}) => (\n \n

\n \n ))}\n \n \n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Details.js","children":"import { use, Suspense, ViewTransition } from \"react\"; import { fetchVideo, fetchVideoDetails } from \"./data\"; import { Thumbnail, VideoControls } from \"./Videos\"; import { useRouter } from \"./router\"; import Layout from \"./Layout\"; import { ChevronLeft } from \"./Icons\";\n\nfunction VideoDetails({id}) {\n // Animate from Suspense fallback to content.\n // If this is pre-rendered then the fallback\n // won't need to show.\n return (\n \n \n \n }\n >\n {/* Animate the content up */}\n \n \n \n \n );\n}\n\nfunction VideoInfoFallback() {\n return (\n <>\n

\n \n );\n}\n\nexport default function Details({id}) {\n const { url, navigateBack } = useRouter();\n const video = use(fetchVideo(id));\n\n return (\n {\n navigateBack(\"/\");\n }}\n >\n Back\n \n }\n >\n

\n \n \n \n \n

\n \n );\n}\n\nfunction VideoInfo({ id }) {\n const details = use(fetchVideoDetails(id));\n return (\n <>\n

{details.title}

{details.description}

\n {filteredVideos.length === 0 && (\n

No results

\n )}\n

\n {filteredVideos.map((video) => (\n // Animate each item in list (\"what\")\n \n

\n ))}\n

\n );\n}\n\nexport default function Home() {\n const videos = use(fetchVideos());\n const count = videos.length;\n const [searchText, setSearchText] = useState('');\n\n return (\n {count} Videos}>\n \n \n \n );\n}\n\nfunction SearchInput({ value, onChange }) {\n const id = useId();\n return (\n \n );\n}\n\nfunction filterVideos(videos, query) {\n const keywords = query\n .toLowerCase()\n .split(\" \")\n .filter((s) => s !== \"\");\n if (keywords.length === 0) {\n return videos;\n }\n return videos.filter((video) => {\n const words = (video.title + \" \" + video.description)\n .toLowerCase()\n .split(\" \");\n return keywords.every((kw) => words.some((w) => w.includes(kw)));\n });\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Icons.js hidden","children":"export function ChevronLeft() {\n return (\n \n \n \n \n \n \n );\n}\n\nexport function PauseIcon() {\n return (\n \n \n \n );\n}\n\nexport function PlayIcon() {\n return (\n \n \n \n );\n}\nexport function Heart({liked, animate}) {\n return (\n <>\n \n \n \n\n \n {liked ? (\n \n ) : (\n \n )}\n \n \n );\n}\n\nexport function IconSearch(props) {\n return (\n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Layout.js hidden","children":"import {ViewTransition} from 'react'; import { useIsNavPending } from \"./router\";\n\nexport default function Page({ heading, children }) {\n const isPending = useIsNavPending();\n return (\n

\n {/* Custom classes based on transition type. */}\n \n {heading}\n \n {isPending && }\n

\n {/* Opt-out of ViewTransition for the content. */}\n {/* Content can define it's own ViewTransition. */}\n \n

{children}

\n \n

\n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/LikeButton.js hidden","children":"import {useState} from 'react';\nimport {Heart} from './Icons';\n\n// A hack since we don't actually have a backend.\n// Unlike local state, this survives videos being filtered.\nconst likedVideos = new Set();\n\nexport default function LikeButton({video}) {\n const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));\n const [animate, setAnimate] = useState(false);\n return (\n {\n const nextIsLiked = !isLiked;\n if (nextIsLiked) {\n likedVideos.add(video.id);\n } else {\n likedVideos.delete(video.id);\n }\n setAnimate(true);\n setIsLiked(nextIsLiked);\n }}>\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/Videos.js hidden","children":"import { useState, ViewTransition } from \"react\";\nimport LikeButton from \"./LikeButton\";\nimport { useRouter } from \"./router\";\nimport { PauseIcon, PlayIcon } from \"./Icons\";\nimport { startTransition } from \"react\";\n\nexport function Thumbnail({ video, children }) {\n // Add a name to animate with a shared element transition.\n // This uses the default animation, no additional css needed.\n return (\n \n \n {children}\n \n \n );\n}\n\nexport function VideoControls() {\n const [isPlaying, setIsPlaying] = useState(false);\n\n return (\n \n startTransition(() => {\n setIsPlaying((p) => !p);\n })\n }\n >\n {isPlaying ? : }\n \n );\n}\n\nexport function Video({ video }) {\n const { navigate } = useRouter();\n\n return (\n

\n {\n e.preventDefault();\n navigate(`/video/${video.id}`);\n }}\n >\n \n\n

{video.title}

{video.description}

\n \n \n );\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/data.js hidden","children":"const videos = [\n {\n id: '1',\n title: 'First video',\n description: 'Video description',\n image: 'blue',\n },\n {\n id: '2',\n title: 'Second video',\n description: 'Video description',\n image: 'red',\n },\n {\n id: '3',\n title: 'Third video',\n description: 'Video description',\n image: 'green',\n },\n {\n id: '4',\n title: 'Fourth video',\n description: 'Video description',\n image: 'purple',\n },\n {\n id: '5',\n title: 'Fifth video',\n description: 'Video description',\n image: 'yellow',\n },\n {\n id: '6',\n title: 'Sixth video',\n description: 'Video description',\n image: 'gray',\n },\n];\n\nlet videosCache = new Map();\nlet videoCache = new Map();\nlet videoDetailsCache = new Map();\nconst VIDEO_DELAY = 1;\nconst VIDEO_DETAILS_DELAY = 1000;\nexport function fetchVideos() {\n if (videosCache.has(0)) {\n return videosCache.get(0);\n }\n const promise = new Promise((resolve) => {\n setTimeout(() => {\n resolve(videos);\n }, VIDEO_DELAY);\n });\n videosCache.set(0, promise);\n return promise;\n}\n\nexport function fetchVideo(id) {\n if (videoCache.has(id)) {\n return videoCache.get(id);\n }\n const promise = new Promise((resolve) => {\n setTimeout(() => {\n resolve(videos.find((video) => video.id === id));\n }, VIDEO_DELAY);\n });\n videoCache.set(id, promise);\n return promise;\n}\n\nexport function fetchVideoDetails(id) {\n if (videoDetailsCache.has(id)) {\n return videoDetailsCache.get(id);\n }\n const promise = new Promise((resolve) => {\n setTimeout(() => {\n resolve(videos.find((video) => video.id === id));\n }, VIDEO_DETAILS_DELAY);\n });\n videoDetailsCache.set(id, promise);\n return promise;\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/router.js hidden","children":"import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, addTransitionType} from \"react\";\n\nexport function Router({ children }) {\n const [isPending, startTransition] = useTransition();\n const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});\n function navigate(url) {\n startTransition(() => {\n // Transition type for the cause \"nav forward\"\n addTransitionType('nav-forward');\n go(url);\n });\n }\n function navigateBack(url) {\n startTransition(() => {\n // Transition type for the cause \"nav backward\"\n addTransitionType('nav-back');\n go(url);\n });\n }\n\n function go(url) {\n setRouterState({\n url,\n pendingNav() {\n window.history.pushState({}, \"\", url);\n },\n });\n }\n\n useEffect(() => {\n function handlePopState() {\n // This should not animate because restoration has to be synchronous.\n // Even though it's a transition.\n startTransition(() => {\n setRouterState({\n url: document.location.pathname + document.location.search,\n pendingNav() {\n // Noop. URL has already updated.\n },\n });\n });\n }\n window.addEventListener(\"popstate\", handlePopState);\n return () => {\n window.removeEventListener(\"popstate\", handlePopState);\n };\n }, []);\n const pendingNav = routerState.pendingNav;\n useLayoutEffect(() => {\n pendingNav();\n }, [pendingNav]);\n\n return (\n \n {children}\n \n );\n}\n\nconst RouterContext = createContext({ url: \"/\", params: {} });\n\nexport function useRouter() {\n return use(RouterContext);\n}\n\nexport function useIsNavPending() {\n return use(RouterContext).isPending;\n}\n\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-css","meta":"src/styles.css hidden","children":"@font-face {\n font-family: Optimistic Text;\n src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format(\"woff2\");\n font-weight: 400;\n font-style: normal;\n font-display: swap;\n}\n\n@font-face {\n font-family: Optimistic Text;\n src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format(\"woff2\");\n font-weight: 500;\n font-style: normal;\n font-display: swap;\n}\n\n@font-face {\n font-family: Optimistic Text;\n src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format(\"woff2\");\n font-weight: 600;\n font-style: normal;\n font-display: swap;\n}\n\n@font-face {\n font-family: Optimistic Text;\n src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format(\"woff2\");\n font-weight: 700;\n font-style: normal;\n font-display: swap;\n}\n\n* {\n box-sizing: border-box;\n}\n\nhtml {\n background-image: url(https://react.dev/images/meta-gradient-dark.png);\n background-size: 100%;\n background-position: -100%;\n background-color: rgb(64 71 86);\n background-repeat: no-repeat;\n height: 100%;\n width: 100%;\n}\n\nbody {\n font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;\n padding: 10px 0 10px 0;\n margin: 0;\n display: flex;\n justify-content: center;\n}\n\n#root {\n flex: 1 1;\n height: auto;\n background-color: #fff;\n border-radius: 10px;\n max-width: 450px;\n min-height: 600px;\n padding-bottom: 10px;\n}\n\nh1 {\n margin-top: 0;\n font-size: 22px;\n}\n\nh2 {\n margin-top: 0;\n font-size: 20px;\n}\n\nh3 {\n margin-top: 0;\n font-size: 18px;\n}\n\nh4 {\n margin-top: 0;\n font-size: 16px;\n}\n\nh5 {\n margin-top: 0;\n font-size: 14px;\n}\n\nh6 {\n margin-top: 0;\n font-size: 12px;\n}\n\ncode {\n font-size: 1.2em;\n}\n\nul {\n padding-inline-start: 20px;\n}\n\n.sr-only {\n position: absolute;\n width: 1px;\n height: 1px;\n padding: 0;\n margin: -1px;\n overflow: hidden;\n clip: rect(0, 0, 0, 0);\n white-space: nowrap;\n border-width: 0;\n}\n\n.absolute {\n position: absolute;\n}\n\n.overflow-visible {\n overflow: visible;\n}\n\n.visible {\n overflow: visible;\n}\n\n.fit {\n width: fit-content;\n}\n\n\n/* Layout */\n.page {\n display: flex;\n flex-direction: column;\n height: 100%;\n}\n\n.top-hero {\n height: 200px;\n display: flex;\n justify-content: center;\n align-items: center;\n background-image: conic-gradient(\n from 90deg at -10% 100%,\n #2b303b 0deg,\n #2b303b 90deg,\n #16181d 1turn\n );\n}\n\n.bottom {\n flex: 1;\n overflow: auto;\n}\n\n.top-nav {\n display: flex;\n align-items: center;\n justify-content: space-between;\n margin-bottom: 0;\n padding: 0 12px;\n top: 0;\n width: 100%;\n height: 44px;\n color: #23272f;\n font-weight: 700;\n font-size: 20px;\n z-index: 100;\n cursor: default;\n}\n\n.content {\n padding: 0 12px;\n margin-top: 4px;\n}\n\n\n.loader {\n color: #23272f;\n font-size: 3px;\n width: 1em;\n margin-right: 18px;\n height: 1em;\n border-radius: 50%;\n position: relative;\n text-indent: -9999em;\n animation: loading-spinner 1.3s infinite linear;\n animation-delay: 200ms;\n transform: translateZ(0);\n}\n\n@keyframes loading-spinner {\n 0%,\n 100% {\n box-shadow: 0 -3em 0 0.2em,\n 2em -2em 0 0em, 3em 0 0 -1em,\n 2em 2em 0 -1em, 0 3em 0 -1em,\n -2em 2em 0 -1em, -3em 0 0 -1em,\n -2em -2em 0 0;\n }\n 12.5% {\n box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,\n 3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,\n -2em 2em 0 -1em, -3em 0 0 -1em,\n -2em -2em 0 -1em;\n }\n 25% {\n box-shadow: 0 -3em 0 -0.5em,\n 2em -2em 0 0, 3em 0 0 0.2em,\n 2em 2em 0 0, 0 3em 0 -1em,\n -2em 2em 0 -1em, -3em 0 0 -1em,\n -2em -2em 0 -1em;\n }\n 37.5% {\n box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,\n 3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,\n -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;\n }\n 50% {\n box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,\n 3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,\n -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;\n }\n 62.5% {\n box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,\n 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,\n -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;\n }\n 75% {\n box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,\n 3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,\n -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;\n }\n 87.5% {\n box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,\n 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,\n -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;\n }\n}\n\n/* LikeButton */\n.like-button {\n outline-offset: 2px;\n position: relative;\n display: flex;\n align-items: center;\n justify-content: center;\n width: 2.5rem;\n height: 2.5rem;\n cursor: pointer;\n border-radius: 9999px;\n border: none;\n outline: none 2px;\n color: #5e687e;\n background: none;\n}\n\n.like-button:focus {\n color: #a6423a;\n background-color: rgba(166, 66, 58, .05);\n}\n\n.like-button:active {\n color: #a6423a;\n background-color: rgba(166, 66, 58, .05);\n transform: scaleX(0.95) scaleY(0.95);\n}\n\n.like-button:hover {\n background-color: #f6f7f9;\n}\n\n.like-button.liked {\n color: #a6423a;\n}\n\n/* Icons */\n@keyframes circle {\n 0% {\n transform: scale(0);\n stroke-width: 16px;\n }\n\n 50% {\n transform: scale(.5);\n stroke-width: 16px;\n }\n\n to {\n transform: scale(1);\n stroke-width: 0;\n }\n}\n\n.circle {\n color: rgba(166, 66, 58, .5);\n transform-origin: center;\n transition-property: all;\n transition-duration: .15s;\n transition-timing-function: cubic-bezier(.4,0,.2,1);\n}\n\n.circle.liked.animate {\n animation: circle .3s forwards;\n}\n\n.heart {\n width: 1.5rem;\n height: 1.5rem;\n}\n\n.heart.liked {\n transform-origin: center;\n transition-property: all;\n transition-duration: .15s;\n transition-timing-function: cubic-bezier(.4, 0, .2, 1);\n}\n\n.heart.liked.animate {\n animation: scale .35s ease-in-out forwards;\n}\n\n.control-icon {\n color: hsla(0, 0%, 100%, .5);\n filter: drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));\n}\n\n.chevron-left {\n margin-top: 2px;\n rotate: 90deg;\n}\n\n\n/* Video */\n.thumbnail {\n position: relative;\n aspect-ratio: 16 / 9;\n display: flex;\n overflow: hidden;\n flex-direction: column;\n justify-content: center;\n align-items: center;\n border-radius: 0.5rem;\n outline-offset: 2px;\n width: 8rem;\n vertical-align: middle;\n background-color: #ffffff;\n background-size: cover;\n user-select: none;\n}\n\n.thumbnail.blue {\n background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);\n}\n\n.thumbnail.red {\n background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);\n}\n\n.thumbnail.green {\n background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);\n}\n\n.thumbnail.purple {\n background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);\n}\n\n.thumbnail.yellow {\n background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);\n}\n\n.thumbnail.gray {\n background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);\n}\n\n.video {\n display: flex;\n flex-direction: row;\n gap: 0.75rem;\n align-items: center;\n}\n\n.video .link {\n display: flex;\n flex-direction: row;\n flex: 1 1 0;\n gap: 0.125rem;\n outline-offset: 4px;\n cursor: pointer;\n}\n\n.video .info {\n display: flex;\n flex-direction: column;\n justify-content: center;\n margin-left: 8px;\n gap: 0.125rem;\n}\n\n.video .info:hover {\n text-decoration: underline;\n}\n\n.video-title {\n font-size: 15px;\n line-height: 1.25;\n font-weight: 700;\n color: #23272f;\n}\n\n.video-description {\n color: #5e687e;\n font-size: 13px;\n}\n\n/* Details */\n.details .thumbnail {\n position: relative;\n aspect-ratio: 16 / 9;\n display: flex;\n overflow: hidden;\n flex-direction: column;\n justify-content: center;\n align-items: center;\n border-radius: 0.5rem;\n outline-offset: 2px;\n width: 100%;\n vertical-align: middle;\n background-color: #ffffff;\n background-size: cover;\n user-select: none;\n}\n\n.video-details-title {\n margin-top: 8px;\n}\n\n.video-details-speaker {\n display: flex;\n gap: 8px;\n margin-top: 10px\n}\n\n.back {\n display: flex;\n align-items: center;\n margin-left: -5px;\n cursor: pointer;\n}\n\n.back:hover {\n text-decoration: underline;\n}\n\n.info-title {\n font-size: 1.5rem;\n font-weight: 700;\n line-height: 1.25;\n margin: 8px 0 0 0 ;\n}\n\n.info-description {\n margin: 8px 0 0 0;\n}\n\n.controls {\n cursor: pointer;\n}\n\n.fallback {\n background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;\n background-size: 800px 104px;\n display: block;\n line-height: 1.25;\n margin: 8px 0 0 0;\n border-radius: 5px;\n overflow: hidden;\n\n animation: 1s linear 1s infinite shimmer;\n animation-delay: 300ms;\n animation-duration: 1s;\n animation-fill-mode: forwards;\n animation-iteration-count: infinite;\n animation-name: shimmer;\n animation-timing-function: linear;\n}\n\n\n.fallback.title {\n width: 130px;\n height: 30px;\n\n}\n\n.fallback.description {\n width: 150px;\n height: 21px;\n}\n\n@keyframes shimmer {\n 0% {\n background-position: -468px 0;\n }\n\n 100% {\n background-position: 468px 0;\n }\n}\n\n.search {\n margin-bottom: 10px;\n}\n.search-input {\n width: 100%;\n position: relative;\n}\n\n.search-icon {\n position: absolute;\n top: 0;\n bottom: 0;\n inset-inline-start: 0;\n display: flex;\n align-items: center;\n padding-inline-start: 1rem;\n pointer-events: none;\n color: #99a1b3;\n}\n\n.search-input input {\n display: flex;\n padding-inline-start: 2.75rem;\n padding-top: 10px;\n padding-bottom: 10px;\n width: 100%;\n text-align: start;\n background-color: rgb(235 236 240);\n outline: 2px solid transparent;\n cursor: pointer;\n border: none;\n align-items: center;\n color: rgb(35 39 47);\n border-radius: 9999px;\n vertical-align: middle;\n font-size: 15px;\n}\n\n.search-input input:hover, .search-input input:active {\n background-color: rgb(235 236 240/ 0.8);\n color: rgb(35 39 47/ 0.8);\n}\n\n/* Home */\n.video-list {\n position: relative;\n}\n\n.video-list .videos {\n display: flex;\n flex-direction: column;\n gap: 1rem;\n overflow-y: auto;\n height: 100%;\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-css","meta":"src/animations.css","children":"/* No additional animations needed */\n\n\n\n\n\n\n\n\n\n/* Previously defined animations below */\n\n\n\n\n\n\n/* Slide animations for Suspense the fallback down */\n::view-transition-old(.slide-down) {\n animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;\n}\n\n::view-transition-new(.slide-up) {\n animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;\n}\n\n/* Animations for view transition classed added by transition type */\n::view-transition-old(.slide-forward) {\n /* when sliding forward, the \"old\" page should slide out to left. */\n animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,\n 400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;\n}\n\n::view-transition-new(.slide-forward) {\n /* when sliding forward, the \"new\" page should slide in from right. */\n animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,\n 400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;\n}\n\n::view-transition-old(.slide-back) {\n /* when sliding back, the \"old\" page should slide out to right. */\n animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,\n 400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;\n}\n\n::view-transition-new(.slide-back) {\n /* when sliding back, the \"new\" page should slide in from left. */\n animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,\n 400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;\n}\n\n/* Keyframes to support our animations above. */\n@keyframes slide-up {\n from {\n transform: translateY(10px);\n }\n to {\n transform: translateY(0);\n }\n}\n\n@keyframes slide-down {\n from {\n transform: translateY(0);\n }\n to {\n transform: translateY(10px);\n }\n}\n\n@keyframes fade-in {\n from {\n opacity: 0;\n }\n}\n\n@keyframes fade-out {\n to {\n opacity: 0;\n }\n}\n\n@keyframes slide-to-right {\n to {\n transform: translateX(50px);\n }\n}\n\n@keyframes slide-from-right {\n from {\n transform: translateX(50px);\n }\n to {\n transform: translateX(0);\n }\n}\n\n@keyframes slide-to-left {\n to {\n transform: translateX(-50px);\n }\n}\n\n@keyframes slide-from-left {\n from {\n transform: translateX(-50px);\n }\n to {\n transform: translateX(0);\n }\n}\n\n/* Default .slow-fade. */\n::view-transition-old(.slow-fade) {\n animation-duration: 500ms;\n}\n\n::view-transition-new(.slow-fade) {\n animation-duration: 500ms;\n}\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","meta":"src/index.js hidden","children":"import React, {StrictMode} from 'react';\nimport {createRoot} from 'react-dom/client';\nimport './styles.css';\nimport './animations.css';\n\nimport App from './App';\nimport {Router} from './router';\n\nconst root = createRoot(document.getElementById('root'));\nroot.render(\n \n \n \n \n \n);\n"}]}],["$r","pre",null,{"children":["$r","code",null,{"className":"language-json","meta":"package.json hidden","children":"{\n \"dependencies\": {\n \"react\": \"canary\",\n \"react-dom\": \"canary\",\n \"react-scripts\": \"latest\"\n },\n \"scripts\": {\n \"start\": \"react-scripts start\",\n \"build\": \"react-scripts build\",\n \"test\": \"react-scripts test --env=jsdom\",\n \"eject\": \"react-scripts eject\"\n }\n}\n"}]}]]}],["$r","MaxWidth","last",{"children":["\n",["$r","h3",null,{"id":"server-side-rendering-with-activity","children":"Server-Side Rendering with Activity "}],"\n",["$r","p",null,{"children":"When using Activity on a page that uses server-side rendering (SSR), there are additional optimizations."}],"\n",["$r","p",null,{"children":["If part of the page is rendered with ",["$r","code",null,{"children":"mode=\"hidden\""}],", then it will not be included in the SSR response. Instead, React will schedule a client render for the content inside Activity while the rest of the page hydrates, prioritizing the visible content on screen."]}],"\n",["$r","p",null,{"children":["For parts of the UI rendered with ",["$r","code",null,{"children":"mode=\"visible\""}],", React will de-prioritize hydration of content within Activity, similar to how Suspense content is hydrated at a lower priority. If the user interacts with the page, we’ll prioritize hydration within the boundary if needed."]}],"\n",["$r","p",null,{"children":"These are advanced use cases, but they show the additional benefits considered with Activity."}],"\n",["$r","h3",null,{"id":"future-modes-for-activity","children":"Future modes for Activity "}],"\n",["$r","p",null,{"children":"In the future, we may add more modes to Activity."}],"\n",["$r","p",null,{"children":"For example, a common use case is rendering a modal, where the previous “inactive” page is visible behind the “active” modal view. The “hidden” mode does not work for this use case because it’s not visible and not included in SSR."}],"\n",["$r","p",null,{"children":"Instead, we’re considering a new mode that would keep the content visible—and included in SSR—but keep it unmounted and de-prioritize updates. This mode may also need to “pause” DOM updates, since it can be distracting to see backgrounded content updating while a modal is open."}],"\n",["$r","p",null,{"children":"Another mode we’re considering for Activity is the ability to automatically destroy state for hidden Activities if there is too much memory being used. Since the component is already unmounted, it may be preferable to destroy state for the least recently used hidden parts of the app rather than consume too many resources."}],"\n",["$r","p",null,{"children":["These are areas we’re still exploring, and we’ll share more as we make progress. For more information on what Activity includes today, ",["$r","a",null,{"href":"/reference/react/Activity","children":"check out the docs"}],"."]}],"\n",["$r","hr",null,{}],"\n",["$r","h1",null,{"id":"features-in-development","children":"Features in development "}],"\n",["$r","p",null,{"children":"We’re also developing features to help solve the common problems below."}],"\n",["$r","p",null,{"children":"As we iterate on possible solutions, you may see some potential APIs we’re testing being shared based on the PRs we are landing. Please keep in mind that as we try different ideas, we often change or remove different solutions after trying them out."}],"\n",["$r","p",null,{"children":"When the solutions we’re working on are shared too early, it can create churn and confusion in the community. To balance being transparent and limiting confusion, we’re sharing the problems we’re currently developing solutions for, without sharing a particular solution we have in mind."}],"\n",["$r","p",null,{"children":"As these features progress, we’ll announce them on the blog with docs included so you can try them out."}],"\n",["$r","h2",null,{"id":"react-performance-tracks","children":"React Performance Tracks "}],"\n",["$r","p",null,{"children":["We’re working on a new set of custom tracks to performance profilers using browser APIs that ",["$r","a",null,{"href":"https://developer.chrome.com/docs/devtools/performance/extension","target":"_blank","rel":"nofollow noopener noreferrer","children":"allow adding custom tracks"}]," to provide more information about the performance of your React app."]}],"\n",["$r","p",null,{"children":"This feature is still in progress, so we’re not ready to publish docs to fully release it as an experimental feature yet. You can get a sneak preview when using an experimental version of React, which will automatically add the performance tracks to profiles:"}],"\n",["$r","div",null,{"style":{"display":"flex","justifyContent":"center","marginBottom":"1rem"},"children":[["$r","picture",null,{"children":[["$r","source",null,{"srcset":"/images/blog/react-labs-april-2025/perf_tracks.png"}],["$r","img",null,{"className":"w-full light-image","src":"/images/blog/react-labs-april-2025/perf_tracks.webp"}]]}],["$r","picture",null,{"children":[["$r","source",null,{"srcset":"/images/blog/react-labs-april-2025/perf_tracks_dark.png"}],["$r","img",null,{"className":"w-full dark-image","src":"/images/blog/react-labs-april-2025/perf_tracks_dark.webp"}]]}]]}],"\n",["$r","p",null,{"children":"There are a few known issues we plan to address such as performance, and the scheduler track not always “connecting” work across Suspended trees, so it’s not quite ready to try. We’re also still collecting feedback from early adopters to improve the design and usability of the tracks."}],"\n",["$r","p",null,{"children":"Once we solve those issues, we’ll publish experimental docs and share that it’s ready to try."}],"\n",["$r","hr",null,{}],"\n",["$r","h2",null,{"id":"automatic-effect-dependencies","children":"Automatic Effect Dependencies "}],"\n",["$r","p",null,{"children":"When we released hooks, we had three motivations:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Sharing code between components"}],": hooks replaced patterns like render props and higher-order components to allow you to reuse stateful logic without changing your component hierarchy."]}],"\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Think in terms of function, not lifecycles"}],": hooks let you split one component into smaller functions based on what pieces are related (such as setting up a subscription or fetching data), rather than forcing a split based on lifecycle methods."]}],"\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Support ahead-of-time compilation"}],": hooks were designed to support ahead-of-time compilation with less pitfalls causing unintentional de-optimizations caused by lifecycle methods, and limitations of classes."]}],"\n"]}],"\n",["$r","p",null,{"children":["Since their release, hooks have been successful at ",["$r","em",null,{"children":"sharing code between components"}],". Hooks are now the favored way to share logic between components, and there are less use cases for render props and higher order components. Hooks have also been successful at supporting features like Fast Refresh that were not possible with class components."]}],"\n",["$r","h3",null,{"id":"effects-can-be-hard","children":"Effects can be hard "}],"\n",["$r","p",null,{"children":"Unfortunately, some hooks are still hard to think in terms of function instead of lifecycles. Effects specifically are still hard to understand and are the most common pain point we hear from developers. Last year, we spent a significant amount of time researching how Effects were used, and how those use cases could be simplified and easier to understand."}],"\n",["$r","p",null,{"children":["We found that often, the confusion is from using an Effect when you don’t need to. The ",["$r","a",null,{"href":"/learn/you-might-not-need-an-effect","children":"You Might Not Need an Effect"}]," guide covers many cases for when Effects are not the right solution. However, even when an Effect is the right fit for a problem, Effects can still be harder to understand than class component lifecycles."]}],"\n",["$r","p",null,{"children":["We believe one of the reasons for confusion is that developers to think of Effects from the ",["$r","em",null,{"children":"component’s"}]," perspective (like a lifecycle), instead of the ",["$r","em",null,{"children":"Effects"}]," point of view (what the Effect does)."]}],"\n",["$r","p",null,{"children":["Let’s look at an example ",["$r","a",null,{"href":"/learn/lifecycle-of-reactive-effects#thinking-from-the-effects-perspective","children":"from the docs"}],":"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","children":"useEffect(() => {\n // Your Effect connected to the room specified with roomId...\n const connection = createConnection(serverUrl, roomId);\n connection.connect();\n return () => {\n // ...until it disconnected\n connection.disconnect();\n };\n}, [roomId]);\n"}]}],"\n",["$r","p",null,{"children":["Many users would read this code as “on mount, connect to the roomId. whenever ",["$r","code",null,{"children":"roomId"}]," changes, disconnect to the old room and re-create the connection”. However, this is thinking from the component’s lifecycle perspective, which means you will need to think of every component lifecycle state to write the Effect correctly. This can be difficult, so it’s understandable that Effects seem harder than class lifecycles when using the component perspective."]}],"\n",["$r","h3",null,{"id":"effects-without-dependencies","children":"Effects without dependencies "}],"\n",["$r","p",null,{"children":"Instead, it’s better to think from the Effect’s perspective. The Effect doesn’t know about the component lifecycles. It only describes how to start synchronization and how to stop it. When users think of Effects in this way, their Effects tend to be easier to write, and more resilient to being started and stopped as many times as is needed."}],"\n",["$r","p",null,{"children":"We spent some time researching why Effects are thought of from the component perspective, and we think one of the reasons is the dependency array. Since you have to write it, it’s right there and in your face reminding you of what you’re “reacting” to and baiting you into the mental model of ‘do this when these values change’."}],"\n",["$r","p",null,{"children":["When we released hooks, we knew we could make them easier to use with ahead-of-time compilation. With the React Compiler, you’re now able to avoid writing ",["$r","code",null,{"children":"useCallback"}]," and ",["$r","code",null,{"children":"useMemo"}]," yourself in most cases. For Effects, the compiler can insert the dependencies for you:"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","children":"useEffect(() => {\n const connection = createConnection(serverUrl, roomId);\n connection.connect();\n return () => {\n connection.disconnect();\n };\n}); // compiler inserted dependencies.\n"}]}],"\n",["$r","p",null,{"children":["With this code, the React Compiler can infer the dependencies for you and insert them automatically so you don’t need to see or write them. With features like ",["$r","a",null,{"href":"#compiler-ide-extension","children":"the IDE extension"}]," and ",["$r","a",null,{"href":"/reference/react/useEffectEvent","children":["$r","code",null,{"children":"useEffectEvent"}]}],", we can provide a CodeLens to show you what the Compiler inserted for times you need to debug, or to optimize by removing a dependency. This helps reinforce the correct mental model for writing Effects, which can run at any time to synchronize your component or hook’s state with something else."]}],"\n",["$r","p",null,{"children":"Our hope is that automatically inserting dependencies is not only easier to write, but that it also makes them easier to understand by forcing you to think in terms of what the Effect does, and not in component lifecycles."}],"\n",["$r","hr",null,{}],"\n",["$r","h2",null,{"id":"compiler-ide-extension","children":"Compiler IDE Extension "}],"\n",["$r","p",null,{"children":["Later in 2025 ",["$r","a",null,{"href":"/blog/2025/10/07/react-compiler-1","children":"we shared"}]," the first stable release of React Compiler, and we’re continuing to invest in shipping more improvements."]}],"\n",["$r","p",null,{"children":["We’ve also begun exploring ways to use the React Compiler to provide information that can improve understanding and debugging your code. One idea we’ve started exploring is a new experimental LSP-based React IDE extension powered by React Compiler, similar to the extension used in ",["$r","a",null,{"href":"https://conf2024.react.dev/talks/5","target":"_blank","rel":"nofollow noopener noreferrer","children":"Lauren Tan’s React Conf talk"}],"."]}],"\n",["$r","p",null,{"children":["Our idea is that we can use the compiler’s static analysis to provide more information, suggestions, and optimization opportunities directly in your IDE. For example, we can provide diagnostics for code breaking the Rules of React, hovers to show if components and hooks were optimized by the compiler, or a CodeLens to see ",["$r","a",null,{"href":"#automatic-effect-dependencies","children":"automatically inserted Effect dependencies"}],"."]}],"\n",["$r","p",null,{"children":"The IDE extension is still an early exploration, but we’ll share our progress in future updates."}],"\n",["$r","hr",null,{}],"\n",["$r","h2",null,{"id":"fragment-refs","children":"Fragment Refs "}],"\n",["$r","p",null,{"children":["Many DOM APIs like those for event management, positioning, and focus are difficult to compose when writing with React. This often leads developers to reach for Effects, managing multiple Refs, by using APIs like ",["$r","code",null,{"children":"findDOMNode"}]," (removed in React 19)."]}],"\n",["$r","p",null,{"children":"We are exploring adding refs to Fragments that would point to a group of DOM elements, rather than just a single element. Our hope is that this will simplify managing multiple children and make it easier to write composable React code when calling DOM APIs."}],"\n",["$r","p",null,{"children":"Fragment refs are still being researched. We’ll share more when we’re closer to having the final API finished."}],"\n",["$r","hr",null,{}],"\n",["$r","h2",null,{"id":"gesture-animations","children":"Gesture Animations "}],"\n",["$r","p",null,{"children":"We’re also researching ways to enhance View Transitions to support gesture animations such as swiping to open a menu, or scroll through a photo carousel."}],"\n",["$r","p",null,{"children":"Gestures present new challenges for a few reasons:"}],"\n",["$r","ul",null,{"children":["\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Gestures are continuous"}],": as you swipe the animation is tied to your finger placement time, rather than triggering and running to completion."]}],"\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Gestures don’t complete"}],": when you release your finger gesture animations can run to completion, or revert to their original state (like when you only partially open a menu) depending on how far you go."]}],"\n",["$r","li",null,{"children":[["$r","strong",null,{"children":"Gestures invert old and new"}],": while you’re animating, you want the page you are animating from to stay “alive” and interactive. This inverts the browser View Transition model where the “old” state is a snapshot and the “new” state is the live DOM."]}],"\n"]}],"\n",["$r","p",null,{"children":["We believe we’ve found an approach that works well and may introduce a new API for triggering gesture transitions. For now, we’re focused on shipping ",["$r","code",null,{"children":""}],", and will revisit gestures afterward."]}],"\n",["$r","hr",null,{}],"\n",["$r","h2",null,{"id":"concurrent-stores","children":"Concurrent Stores "}],"\n",["$r","p",null,{"children":["When we released React 18 with concurrent rendering, we also released ",["$r","code",null,{"children":"useSyncExternalStore"}]," so external store libraries that did not use React state or context could ",["$r","a",null,{"href":"https://github.com/reactwg/react-18/discussions/70","target":"_blank","rel":"nofollow noopener noreferrer","children":"support concurrent rendering"}]," by forcing a synchronous render when the store is updated."]}],"\n",["$r","p",null,{"children":["Using ",["$r","code",null,{"children":"useSyncExternalStore"}]," comes at a cost though, since it forces a bail out from concurrent features like transitions, and forces existing content to show Suspense fallbacks."]}],"\n",["$r","p",null,{"children":["Now that React 19 has shipped, we’re revisiting this problem space to create a primitive to fully support concurrent external stores with the ",["$r","code",null,{"children":"use"}]," API:"]}],"\n",["$r","pre",null,{"children":["$r","code",null,{"className":"language-js","children":"const value = use(store);\n"}]}],"\n",["$r","p",null,{"children":"Our goal is to allow external state to be read during render without tearing, and to work seamlessly with all of the concurrent features React offers."}],"\n",["$r","p",null,{"children":"This research is still early. We’ll share more, and what the new APIs will look like, when we’re further along."}],"\n",["$r","hr",null,{}],"\n",["$r","p",null,{"children":["$r","em",null,{"children":["Thanks to ",["$r","a",null,{"href":"https://bsky.app/profile/aurorascharff.no","target":"_blank","rel":"nofollow noopener noreferrer","children":"Aurora Scharff"}],", ",["$r","a",null,{"href":"https://bsky.app/profile/danabra.mov","target":"_blank","rel":"nofollow noopener noreferrer","children":"Dan Abramov"}],", ",["$r","a",null,{"href":"https://twitter.com/Eli_White","target":"_blank","rel":"nofollow noopener noreferrer","children":"Eli White"}],", ",["$r","a",null,{"href":"https://bsky.app/profile/no.lol","target":"_blank","rel":"nofollow noopener noreferrer","children":"Lauren Tan"}],", ",["$r","a",null,{"href":"https://github.com/lunaleaps","target":"_blank","rel":"nofollow noopener noreferrer","children":"Luna Wei"}],", ",["$r","a",null,{"href":"https://twitter.com/mattcarrollcode","target":"_blank","rel":"nofollow noopener noreferrer","children":"Matt Carroll"}],", ",["$r","a",null,{"href":"https://jackpope.me","target":"_blank","rel":"nofollow noopener noreferrer","children":"Jack Pope"}],", ",["$r","a",null,{"href":"https://threads.net/someextent","target":"_blank","rel":"nofollow noopener noreferrer","children":"Jason Bonta"}],", ",["$r","a",null,{"href":"https://github.com/jbrown215","target":"_blank","rel":"nofollow noopener noreferrer","children":"Jordan Brown"}],", ",["$r","a",null,{"href":"https://bsky.app/profile/capt.dev","target":"_blank","rel":"nofollow noopener noreferrer","children":"Jordan Eldredge"}],", ",["$r","a",null,{"href":"https://threads.net/z_mofei","target":"_blank","rel":"nofollow noopener noreferrer","children":"Mofei Zhang"}],", ",["$r","a",null,{"href":"https://bsky.app/profile/sebastienlorber.com","target":"_blank","rel":"nofollow noopener noreferrer","children":"Sebastien Lorber"}],", ",["$r","a",null,{"href":"https://bsky.app/profile/sebmarkbage.calyptus.eu","target":"_blank","rel":"nofollow noopener noreferrer","children":"Sebastian Markbåge"}],", and ",["$r","a",null,{"href":"https://github.com/yungsters","target":"_blank","rel":"nofollow noopener noreferrer","children":"Tim Yung"}]," for reviewing this post."]}]}]]}]]