diff --git a/src/content/reference/dev-tools/react-devtools-cdt-mcp.md b/src/content/reference/dev-tools/react-devtools-cdt-mcp.md new file mode 100644 index 000000000..9c966a0ff --- /dev/null +++ b/src/content/reference/dev-tools/react-devtools-cdt-mcp.md @@ -0,0 +1,407 @@ +--- +title: React DevTools for agents +version: experimental +--- + + + +**`react-devtools-cdt-mcp` is experimental.** It is built on the [experimental third-party developer tools API](https://developer.chrome.com/blog/devtools-for-agents-3p-tools) in [Chrome DevTools MCP](https://github.com/ChromeDevTools/chrome-devtools-mcp), and both its tools and their output may change between releases. + + + + + +`react-devtools-cdt-mcp` gives AI coding agents the same view of your app that React DevTools gives you: the component tree, props, hooks, owners, source locations, and render timing. + +```js +import 'react-devtools-cdt-mcp/register'; +``` + + + + + +--- + +## Overview {/*overview*/} + +Coding agents that drive a browser through [Chrome DevTools MCP](https://github.com/ChromeDevTools/chrome-devtools-mcp) can click, take snapshots, and read the DOM, but the DOM doesn't tell them which component rendered a button, what state it holds, or why an interaction was slow. + +`react-devtools-cdt-mcp` is a small browser library that you import into the page you're debugging. It registers a group of React tools with the page. When Chrome DevTools MCP connects to that page, it discovers the tools automatically, and your agent can call them like any other MCP tool. + + + +`react-devtools-cdt-mcp` is **not** an MCP server, and it doesn't go in your MCP client config. It runs inside your page. The only MCP server you configure is Chrome DevTools MCP. + + + +--- + +## Setup {/*setup*/} + +#### Install the package {/*install-the-package*/} + + + +npm install --save-dev react-devtools-cdt-mcp + + + +#### Import it before React {/*import-it-before-react*/} + +Import the `register` entry point at the very top of your app's entry file, **before** anything imports `react-dom`: + +```js {1} +import 'react-devtools-cdt-mcp/register'; + +import { createRoot } from 'react-dom/client'; +import App from './App'; + +createRoot(document.getElementById('root')).render(); +``` + +`react-devtools-cdt-mcp` has to load before React does. If you import it after React, the tools won't see your components. + + + +`react-devtools-cdt-mcp` connects to React the same way the React DevTools extension does, and makes React report every commit to it. This slows down your app, so only include it in development builds. + + + +#### Set up Chrome DevTools MCP {/*set-up-chrome-devtools-mcp*/} + +Your agent needs [Chrome DevTools MCP](https://github.com/ChromeDevTools/chrome-devtools-mcp) with [third-party developer tools](https://developer.chrome.com/blog/devtools-for-agents-3p-tools) enabled. Follow the [Chrome DevTools MCP docs](https://github.com/ChromeDevTools/chrome-devtools-mcp#getting-started) to set it up. Once your agent opens a page that imports `react-devtools-cdt-mcp/register`, it can list and call the React tools. + +--- + +## Try it {/*try-it*/} + +You don't need an agent to see what the tools return. The sandbox below imports `react-devtools-cdt-mcp/register` exactly as you would in your app, and adds a small **tool console** under the app. The console discovers the React tools the same way Chrome DevTools MCP does, by dispatching the `devtoolstooldiscovery` event, and lets you call them by hand. + +Pick a tool, edit the JSON parameters, and press **Run tool**. Here's a debugging session to follow, playing the agent's part: + +1. **Find a component.** Run `react_find_components` with `{"name": "Row"}`. Each result has a `uid`, like `"r12"`, that the other tools accept. +2. **Inspect it.** Run `react_get_component_by_uid` with one of those uids and `"includeHooks": true` to see its props and hooks. +3. **Start from the screen.** Choose `react_get_component_by_dom_element`, press **Pick element**, and click a product in the list to get the host component that rendered it. +4. **Profile an interaction.** Run `react_start_profiling`, click **Add to cart** in the app, then run `react_stop_profiling`. +5. **See what rendered.** Run `react_get_trace_overview`, then `react_get_commit_report` for commit `0` to see which components rendered in that commit and how long each one took. + + + +```js src/App.js active +import { useState } from 'react'; + +const PRODUCTS = Array.from({ length: 20 }, (_, i) => ({ + id: i, + name: 'Product ' + (i + 1), + price: 10 + i, +})); + +export default function App() { + const [query, setQuery] = useState(''); + const visibleProducts = PRODUCTS.filter((product) => + product.name.toLowerCase().includes(query.toLowerCase()) + ); + return ( +
+ + setQuery(e.target.value)} + placeholder="Filter products" + /> + +
+ ); +} + +function Cart() { + const [count, setCount] = useState(0); + return ( +
+ + +
+ ); +} + +function CartBadge({ count }) { + return Cart: {count}; +} + +function ProductList({ products }) { + return ( +
    + {products.map((product) => ( + + ))} +
+ ); +} + +function ProductRow({ product }) { + return ( +
  • + {product.name} ${product.price} +
  • + ); +} +``` + +```js src/index.js +import 'react-devtools-cdt-mcp/register'; + +import { createRoot } from 'react-dom/client'; +import './styles.css'; +import App from './App'; +import { mountToolConsole } from './ToolConsole'; + +createRoot(document.getElementById('root')).render(); +mountToolConsole(); +``` + +```js src/ToolConsole.js hidden +// A tiny stand-in for chrome-devtools-mcp. It discovers the React tool group +// the same way chrome-devtools-mcp does (the `devtoolstooldiscovery` event) +// and lets you call the tools by hand. +function discoverToolGroup() { + let toolGroup = null; + const event = new Event('devtoolstooldiscovery'); + event.respondWith = group => { + toolGroup = group; + }; + window.dispatchEvent(event); + return toolGroup; +} + +function firstUid(tools, name) { + const find = tools.find(t => t.name === 'react_find_components'); + const result = find.execute({name}); + return result.results && result.results[0] ? result.results[0].uid : 'r0'; +} + +function exampleParams(tools, toolName) { + switch (toolName) { + case 'react_get_component_tree': + return {depth: 4}; + case 'react_find_components': + return {name: 'Row'}; + case 'react_get_component_by_uid': + return {uid: firstUid(tools, 'App'), includeHooks: true}; + case 'react_get_component_by_dom_element': + return {element: '(click "Pick element", then click the page)'}; + case 'react_get_component_source': + case 'react_get_owner_stack_trace': + case 'react_get_parent_stack': + case 'react_get_owner_stack': + return {uid: firstUid(tools, 'CartBadge')}; + case 'react_start_profiling': + return {traceName: 'add-to-cart'}; + case 'react_stop_profiling': + return {}; + case 'react_get_trace_overview': + return {traceName: 'add-to-cart'}; + case 'react_get_commit_report': + return {traceName: 'add-to-cart', commitIndex: 0}; + default: + return {}; + } +} + +export function mountToolConsole() { + const toolGroup = discoverToolGroup(); + const container = document.createElement('section'); + container.className = 'tool-console'; + document.body.appendChild(container); + if (toolGroup === null) { + container.textContent = + 'No tools found. Import react-devtools-cdt-mcp/register before React.'; + return; + } + const {tools} = toolGroup; + container.innerHTML = ` +

    Tool console

    + +

    + +
    + + +
    +
    
    +  `;
    +  const select = container.querySelector('select');
    +  const description = container.querySelector('.description');
    +  const textarea = container.querySelector('textarea');
    +  const runButton = container.querySelector('.run');
    +  const pickButton = container.querySelector('.pick');
    +  const output = container.querySelector('pre');
    +  let pickedElement = null;
    +
    +  for (const tool of tools) {
    +    const option = document.createElement('option');
    +    option.value = tool.name;
    +    option.textContent = tool.name;
    +    select.appendChild(option);
    +  }
    +
    +  function selectTool() {
    +    const tool = tools.find(t => t.name === select.value);
    +    description.textContent = tool.description;
    +    textarea.value = JSON.stringify(exampleParams(tools, tool.name));
    +    pickButton.hidden = tool.name !== 'react_get_component_by_dom_element';
    +    pickedElement = null;
    +  }
    +
    +  function run() {
    +    const tool = tools.find(t => t.name === select.value);
    +    let params;
    +    try {
    +      params = JSON.parse(textarea.value || '{}');
    +    } catch (error) {
    +      output.textContent = 'Invalid JSON: ' + error.message;
    +      return;
    +    }
    +    if (tool.name === 'react_get_component_by_dom_element') {
    +      params.element = pickedElement;
    +    }
    +    const result = tool.execute(params);
    +    output.textContent = JSON.stringify(result, null, 2);
    +  }
    +
    +  pickButton.addEventListener('click', () => {
    +    output.textContent = 'Click any element in the app above...';
    +    document.addEventListener(
    +      'click',
    +      event => {
    +        if (container.contains(event.target)) {
    +          return;
    +        }
    +        event.preventDefault();
    +        event.stopPropagation();
    +        pickedElement = event.target;
    +        textarea.value = JSON.stringify({
    +          element: '<' + event.target.tagName.toLowerCase() + '>',
    +        });
    +        run();
    +      },
    +      {capture: true, once: true},
    +    );
    +  });
    +  select.addEventListener('change', selectTool);
    +  runButton.addEventListener('click', run);
    +  selectTool();
    +}
    +```
    +
    +```css src/styles.css hidden
    +header { display: flex; gap: 8px; align-items: center; margin-bottom: 8px; }
    +.badge { padding: 2px 8px; border-radius: 10px; background: #087ea4; color: white; }
    +ul { padding-left: 20px; max-height: 160px; overflow: auto; }
    +.tool-console { margin-top: 20px; padding-top: 12px; border-top: 1px solid #ddd; }
    +.tool-console select, .tool-console textarea { width: 100%; font-family: monospace; }
    +.tool-console .actions { display: flex; gap: 8px; margin: 8px 0; }
    +.tool-console pre { background: #f6f7f9; padding: 8px; max-height: 300px; overflow: auto; }
    +```
    +
    +```json package.json hidden
    +{
    +  "dependencies": {
    +    "react": "latest",
    +    "react-dom": "latest",
    +    "react-scripts": "latest",
    +    "react-devtools-cdt-mcp": "0.0.1"
    +  },
    +  "scripts": {
    +    "start": "react-scripts start",
    +    "build": "react-scripts build",
    +    "test": "react-scripts test --env=jsdom",
    +    "eject": "react-scripts eject"
    +  }
    +}
    +```
    +
    +
    + + + +The tool console in this sandbox stands in for Chrome DevTools MCP so you can try the tools on this page. In your own app, you don't write any of this code: Chrome DevTools MCP discovers the tools and your agent decides which ones to call. + + + +--- + +## Reference {/*reference*/} + +### Tools {/*tools*/} + +`react-devtools-cdt-mcp` registers a tool group called `react`. Your agent calls these tools through Chrome DevTools MCP. + +* `react_get_component_tree`: Returns a snapshot of the component tree. +* `react_find_components`: Finds components by name. +* `react_get_component_by_uid`: Returns a component's props and Hooks. +* `react_get_component_by_dom_element`: Returns the React host component for a DOM element. +* `react_get_parent_stack`: Returns where a component is mounted in the tree. +* `react_get_owner_stack`: Returns the components that created a component in their JSX. +* `react_get_owner_stack_trace`: Returns the owner stack of a component as a stack trace. +* `react_get_component_source`: Returns where a component is defined. +* `react_start_profiling`: Starts recording render timing. +* `react_stop_profiling`: Stops recording render timing. +* `react_get_trace_overview`: Returns a summary of every commit in a recording. +* `react_get_commit_report`: Returns which components rendered in a commit and how long each took. + +Components are identified by short, stable uids like `"r5"`. A uid stays the same across every tool and across re-renders, but not across page reloads. + +Every tool returns a plain, serializable object. If a tool fails, it returns an object with an `error` message instead. + +--- + +### `register(target?)` {/*register*/} + +Call `register` to install the React DevTools hook and register the React tools with Chrome DevTools MCP yourself, instead of importing `react-devtools-cdt-mcp/register`. + +```js +import { register } from 'react-devtools-cdt-mcp'; + +register(); +``` + +#### Parameters {/*register-parameters*/} + +* **optional** `target`: The global object to install the hook on. Defaults to `globalThis`. + +#### Returns {/*register-returns*/} + +`register` returns an object with two properties: + +* `facade`: The installed React DevTools hook and the state the tools read from. +* `unregister`: A function that stops registering the React tools with Chrome DevTools MCP. + +#### Caveats {/*register-caveats*/} + +* Call `register` before React initializes, or React won't connect to the hook. +* Calling `register` again for the same `target` returns the existing registration. + +--- + +## Troubleshooting {/*troubleshooting*/} + +#### My agent doesn't see any React tools {/*my-agent-doesnt-see-any-react-tools*/} + +Check that [third-party developer tools](https://developer.chrome.com/blog/devtools-for-agents-3p-tools) are enabled in your Chrome DevTools MCP setup. Then check that the page selected in Chrome DevTools MCP imports `react-devtools-cdt-mcp/register`. The tools are discovered per page, when the page loads or is selected. + +#### The component tree is empty {/*the-component-tree-is-empty*/} + +`react-devtools-cdt-mcp/register` was imported after React initialized. Move the import to the very first line of your entry file, before any import that loads `react-dom`. + +#### I'm getting an error about a browser-like environment {/*im-getting-an-error-about-a-browser-like-environment*/} + +`react-devtools-cdt-mcp/register` throws if it's imported outside a browser, for example during server rendering or in tests. Import it only from client-side code, or call `register()` from the package root yourself where it's safe. + +#### Source locations and owner stacks are empty {/*source-locations-and-owner-stacks-are-empty*/} + +This data only exists in development builds of React. Make sure you're running your app's development server rather than a production build. + +#### A uid stopped working {/*a-uid-stopped-working*/} + +Uids don't survive page reloads. After a reload, get fresh uids with `react_get_component_tree` or `react_find_components`. diff --git a/src/content/reference/react-dom/components/img.md b/src/content/reference/react-dom/components/img.md index 992b2e0ad..9bc54a2e6 100644 --- a/src/content/reference/react-dom/components/img.md +++ b/src/content/reference/react-dom/components/img.md @@ -56,9 +56,15 @@ Per visualizzare un'immagine, renderizza il [componente browser integrato ` #### Caveats {/*caveats*/} +<<<<<<< HEAD * Non passare una stringa vuota a `src`: potrebbe indurre il browser a richiedere di nuovo la pagina corrente. React mostra un avviso in sviluppo e omette l'attributo. Per non visualizzare alcuna immagine, ometti `` o passa `null` a `src`. * `` non può avere children né usare `dangerouslySetInnerHTML`. React solleva un errore se passi una delle due cose. * `fetchPriority="low"` non impedisce a React di attendere che l'immagine venga caricata e decodificata durante un aggiornamento View Transition renderizzato lato client. Usa `loading="lazy"` o un gestore `onLoad` per rinunciare a questo comportamento. +======= +* Do not pass an empty string to `src`. It may cause the browser to request the current page again. React warns in development and omits the attribute. To render no image, omit the `` or pass `null` to `src`. +* `` cannot have children or use `dangerouslySetInnerHTML`. React throws an error if you pass either. +* `fetchPriority="low"` does not stop React from waiting for the image to load during a client-rendered View Transition update. Use `loading="lazy"` or an `onLoad` handler to opt out of that behavior. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e --- @@ -132,6 +138,7 @@ Per creare un hint di preload esplicito, chiama [`preload`](/reference/react-dom ### Attendere un'immagine durante una View Transition {/*waiting-for-an-image-during-a-view-transition*/} +<<<<<<< HEAD Durante un aggiornamento [``](/reference/react/ViewTransition) renderizzato lato client, React potrebbe attendere che un'immagine si carichi e venga decodificata prima di avviare l'animazione. Questo si applica quando viene renderizzato un nuovo `` con un `src` non vuoto, o quando `src` o `srcSet` di un'immagine esistente cambia. L'immagine deve trovarsi nel sottoalbero del `` e non deve avere `loading="lazy"` né un gestore `onLoad`. React non attende le immagini durante gli aggiornamenti sincroni. Quando un boundary Suspense rivela contenuto in streaming all'interno di un ``, React potrebbe anche attendere le immagini visibili con un `src` non vuoto che non hanno `loading="lazy"`. React smette di attendere dopo un timeout, così che un'immagine lenta non blocchi l'aggiornamento all'infinito. @@ -139,18 +146,28 @@ Quando un boundary Suspense rivela contenuto in streaming all'interno di un `` e mostra un placeholder del profilo finché il ritratto non si è caricato. Per confronto, il secondo pulsante inserisce la stessa card direttamente nel DOM. La card appare immediatamente, e il browser visualizza l'immagine dopo che si è caricata: +======= +During a [``](/reference/react/ViewTransition) update, React waits up to 500 ms for visible images to load before starting the animation. This includes newly rendered `` elements and existing images whose `src` or `srcSet` changes. Setting `loading="lazy"` or adding an `onLoad` handler opts an image out. + +Compare how the same image appears when a Suspense boundary reveals its content inside and outside a ``: +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e ```js -import { ViewTransition, Suspense, useState, startTransition } from 'react'; -import { freshImageUrl } from './image.js'; -import VanillaProfile from './VanillaProfile.js'; - -function Profile({ src }) { +import { + ViewTransition, + Suspense, + use, + useState, +} from 'react'; +import { fetchImageSrc } from './image.js'; + +function Profile({ cacheKey }) { + const src = use(fetchImageSrc(cacheKey)); return (
    - Jack Pope +

    Jack Pope

    ); @@ -166,9 +183,13 @@ function ProfilePlaceholder() { } export default function App() { - const [src, setSrc] = useState(null); + const [showWithTransition, setShowWithTransition] = + useState(false); + const [showWithoutTransition, setShowWithoutTransition] = + useState(false); return ( <> +<<<<<<< HEAD - {src && ( + {showWithTransition && ( }> - + )}
    +<<<<<<< HEAD ); @@ -207,15 +233,42 @@ export default function VanillaProfile() { <>
    +======= + + {showWithoutTransition && ( + }> + + + )} +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e ); } ``` ```js src/image.js hidden +<<<<<<< HEAD // Aggiungi un parametro univoco così l'immagine non finisce in cache // e ogni esecuzione mostra lo stato di caricamento. export function freshImageUrl() { +======= +// Normally, the caching logic would be inside a framework. +const cache = new Map(); + +export function fetchImageSrc(cacheKey) { + if (!cache.has(cacheKey)) { + cache.set(cacheKey, loadImageSrc()); + } + return cache.get(cacheKey); +} + +async function loadImageSrc() { + // Delay the response so the Suspense fallback is visible. + await new Promise(resolve => setTimeout(resolve, 1000)); + // Add a unique parameter so the image isn't cached. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e return 'https://react.dev/images/team/jack-pope.jpg?t=' + Date.now(); } ``` @@ -262,3 +315,5 @@ hr { ``` + +With ``, React keeps the skeleton visible for up to 500 ms while the image loads, so the card can be revealed with its image already in place. Without ``, Suspense stops showing the skeleton as soon as the Promise resolves. If the image is still loading, the card appears first and the image pops in afterward. diff --git a/src/content/reference/react/Suspense.md b/src/content/reference/react/Suspense.md index 23367f8de..9e8726f87 100644 --- a/src/content/reference/react/Suspense.md +++ b/src/content/reference/react/Suspense.md @@ -50,6 +50,7 @@ Questa pagina è stata tradotta automaticamente e supervisionata da un maintaine Un boundary Suspense attende che il suo contenuto sia pronto prima di rivelarlo. Qualsiasi elemento tra i seguenti impedisce a un boundary di rivelare il suo contenuto: +<<<<<<< HEAD - Lazy-loading del codice del componente con [`lazy`](/reference/react/lazy). - Lettura di una Promise con [`use`](/reference/react/use), inclusi dati in streaming da [componenti Server](/reference/rsc/server-components) o caricati tramite un [framework abilitato a Suspense](#suspense-enabled-frameworks). - Caricamento di un foglio di stile renderizzato con [`` e una prop `precedence`.](/reference/react-dom/components/link#special-rendering-behavior) React blocca il boundary finché il foglio di stile non è caricato, fino a un timeout. [Vedi un esempio sotto.](#waiting-for-a-stylesheet-to-load) @@ -57,6 +58,15 @@ Un boundary Suspense attende che il suo contenuto sia pronto prima di rivelarlo. - Caricamento dei font. Suspense non attende i font per impostazione predefinita, ma un aggiornamento con [``](/reference/react/ViewTransition) attende il caricamento dei nuovi font, fino a un timeout, così il testo non lampeggia con un font di fallback. [Vedi un esempio sotto.](#waiting-for-a-font-to-load) - Caricamento delle immagini. Suspense non attende le immagini per impostazione predefinita, ma durante un aggiornamento con [``](/reference/react/ViewTransition), React blocca il boundary finché l'immagine non è caricata, fino a un timeout. Aggiungere un gestore `onLoad` esclude una specifica immagine da questo comportamento. [Vedi un esempio sotto.](#waiting-for-an-image-to-load) - Esecuzione di lavoro di renderizzazione CPU-bound dentro un boundary [``](#props). +======= +- Lazy-loading component code with [`lazy`](/reference/react/lazy). +- Reading a Promise with [`use`](/reference/react/use), including data streamed from [Server Components](/reference/rsc/server-components) or loaded through a [Suspense-enabled framework](#suspense-enabled-frameworks). +- Loading a stylesheet rendered with [`` and a `precedence` prop.](/reference/react-dom/components/link#special-rendering-behavior) React blocks the boundary until the stylesheet loads, up to a timeout. [See an example below.](#waiting-for-a-stylesheet-to-load) +- Waiting for a large boundary's HTML to arrive during streaming server rendering. Sending HTML takes time, so a boundary with enough content activates even when nothing in it suspends. React reveals the content as the HTML arrives. +- Loading fonts. Suspense doesn't wait for fonts by default, but when a [``](/reference/react/ViewTransition) animates a boundary's reveal, React waits up to 500 ms for new fonts to load so text doesn't flash with a fallback font. [See an example below.](#waiting-for-a-font-to-load) +- Loading images. Suspense doesn't wait for images by default, but when a [``](/reference/react/ViewTransition) animates a boundary's reveal, React waits up to 500 ms for visible images to load before starting the animation. Setting `loading="lazy"` or adding an `onLoad` handler opts a specific image out. [See an example below.](#waiting-for-an-image-to-load) +- Performing CPU-bound render work inside a [``](#props) boundary. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e @@ -2908,52 +2918,65 @@ Dove posizioni il `` rispetto al boundary determina se fallback ### Attendere il caricamento di un font {/*waiting-for-a-font-to-load*/} +<<<<<<< HEAD Quando un [``](/reference/react/ViewTransition) anima la rivelazione di un boundary Suspense, React attende i nuovi font introdotti dal contenuto, fino a un timeout, così il testo non lampeggia con un font di fallback. Questo avviene solo durante un aggiornamento con ``. Nell'esempio sotto, il boundary Suspense è avvolto in un `` e il componente `Quote` va in sospensione mentre i suoi dati si caricano. Renderizzare la citazione avvia il download del font. React mantiene visibile il fallback finché il font non è caricato, così la citazione appare già nel suo font. +======= +When a [``](/reference/react/ViewTransition) animates a Suspense boundary's reveal, React waits up to 500 ms for new fonts the content introduces so the text doesn't flash with a fallback font. This only happens during a `` update. + +In the example below, the Suspense boundary is wrapped in a ``, and the `Quote` component suspends while its data loads. Rendering the quote loads a stylesheet that introduces the font. React keeps the fallback visible while the stylesheet and font load. If the font loads within the 500 ms limit, the quote appears already in its font. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e A titolo di confronto, il secondo pulsante esegue lo stesso aggiornamento senza React. Nulla attende il font, quindi il testo appare prima in un font di fallback e poi cambia: ```js -import { ViewTransition, Suspense, use, useState, startTransition } from 'react'; +import { + ViewTransition, + Suspense, + use, + useState, + startTransition, +} from 'react'; import { fetchQuote } from './data.js'; -import { freshFontUrl } from './font.js'; +import { + freshFontUrl, + freshStylesheetUrl, +} from './font.js'; import VanillaQuote from './VanillaQuote.js'; -function Quote({ fontSrc }) { +function Quote({ stylesheet }) { const quote = use(fetchQuote()); return ( <> - +

    {quote}

    ); } export default function App() { - const [fontSrc, setFontSrc] = useState(null); + const [stylesheet, setStylesheet] = useState(null); return ( <> - {fontSrc && ( + {stylesheet && ( ⌛ Loading quote...

    }> - +
    )} @@ -2974,7 +2997,7 @@ export default function VanillaQuote() { const style = document.createElement('style'); style.textContent = `@font-face { font-family: 'VanillaFancy'; - src: url(${freshFontUrl()}) format('truetype'); + src: url(${freshFontUrl()}) format('woff2'); font-display: swap; }`; document.head.appendChild(style); @@ -2990,11 +3013,25 @@ export default function VanillaQuote() { ``` ```js src/font.js hidden +<<<<<<< HEAD // Aggiungi un parametro univoco così il font non è in cache // e ogni esecuzione mostra la fase di caricamento. export function freshFontUrl() { +======= +export function freshStylesheetUrl() { + // Add a unique parameter so the stylesheet isn't cached. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e + return ( + 'https://fonts.googleapis.com/css2?family=Caveat&display=swap' + + '&t=' + + Date.now() + ); +} + +export function freshFontUrl() { + // Add a unique parameter so the font isn't cached. return ( - 'https://raw.githubusercontent.com/google/fonts/main/ofl/caveat/Caveat%5Bwght%5D.ttf' + + 'https://fonts.gstatic.com/s/caveat/v23/WnznHAc5bAfYB2QRah7pcpNvOx-pjfJ9eIWpYT5Kmgq3sw.woff2' + '?t=' + Date.now() ); @@ -3032,7 +3069,7 @@ export function fetchQuote() { margin-top: 1em; } .fancy { - font-family: 'Fancy', sans-serif; + font-family: 'Caveat', sans-serif; } .vanilla-fancy { font-family: 'VanillaFancy', sans-serif; @@ -3045,8 +3082,8 @@ hr { ```json package.json hidden { "dependencies": { - "react": "19.3.0-canary-f1f7ed2a-20260904", - "react-dom": "19.3.0-canary-f1f7ed2a-20260904", + "react": "19.3.0", + "react-dom": "19.3.0", "react-scripts": "latest" } } @@ -3058,23 +3095,34 @@ hr { ### Attendere il caricamento di un'immagine {/*waiting-for-an-image-to-load*/} +<<<<<<< HEAD Quando un [``](/reference/react/ViewTransition) anima la rivelazione di un boundary Suspense, React attende il caricamento delle immagini visibili, fino a un timeout, così l'animazione non inizia con un'immagine a metà caricamento. Questo avviene solo durante un aggiornamento con ``. Aggiungere un gestore `onLoad` esclude una specifica immagine da questo comportamento, anche dentro un ``. Nell'esempio sotto, il boundary Suspense è avvolto in un `` e mostra uno skeleton del profilo finché il ritratto non è caricato. A titolo di confronto, il secondo pulsante esegue lo stesso aggiornamento senza React. Nulla attende l'immagine, quindi la card appare immediatamente e l'immagine compare quando si carica: +======= +When a Suspense boundary reveals content inside a [``](/reference/react/ViewTransition), React waits up to 500 ms for visible images to load before starting the animation. Setting `loading="lazy"` or adding an `onLoad` handler opts an image out. + +Compare the same boundary inside and outside a ``. Inside, React keeps the profile skeleton visible for up to 500 ms while the image loads, so the card can be revealed with its image already in place. Outside, Suspense stops showing the skeleton as soon as the Promise resolves. If the image is still loading, the card appears first and the image pops in afterward: +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e ```js -import { ViewTransition, Suspense, useState, startTransition } from 'react'; -import { freshImageUrl } from './image.js'; -import VanillaProfile from './VanillaProfile.js'; +import { + ViewTransition, + Suspense, + use, + useState, +} from 'react'; +import { fetchImageSrc } from './image.js'; -function Profile({ src }) { +function Profile({ cacheKey }) { + const src = use(fetchImageSrc(cacheKey)); return (
    - Jack Pope +

    Jack Pope

    ); @@ -3090,56 +3138,57 @@ function ProfilePlaceholder() { } export default function App() { - const [src, setSrc] = useState(null); + const [showWithTransition, setShowWithTransition] = + useState(false); + const [showWithoutTransition, setShowWithoutTransition] = + useState(false); return ( <> - - {src && ( + {showWithTransition && ( }> - + )}
    - - - ); -} -``` - -```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 = `
    - Jack Pope -

    Jack Pope

    -
    `; - } - return ( - <> - -
    + + {showWithoutTransition && ( + }> + + + )} ); } ``` ```js src/image.js hidden +<<<<<<< HEAD // Aggiungi un parametro univoco così l'immagine non è in cache // e ogni esecuzione mostra la fase di caricamento. export function freshImageUrl() { +======= +// Normally, the caching logic would be inside a framework. +const cache = new Map(); + +export function fetchImageSrc(cacheKey) { + if (!cache.has(cacheKey)) { + cache.set(cacheKey, loadImageSrc()); + } + return cache.get(cacheKey); +} + +async function loadImageSrc() { + // Delay the response so the Suspense fallback is visible. + await new Promise(resolve => setTimeout(resolve, 1000)); + // Add a unique parameter so the image isn't cached. +>>>>>>> ae5e48074d4f73f1e349eda2a66841f9a959023e return 'https://react.dev/images/team/jack-pope.jpg?t=' + Date.now(); } ``` @@ -3178,8 +3227,8 @@ hr { ```json package.json hidden { "dependencies": { - "react": "19.3.0-canary-f1f7ed2a-20260904", - "react-dom": "19.3.0-canary-f1f7ed2a-20260904", + "react": "19.3.0", + "react-dom": "19.3.0", "react-scripts": "latest" } } @@ -3209,7 +3258,7 @@ function ProfileCard({ resources }) { <>
    - Jack Pope +

    Jack Pope

    {quote}

    @@ -3269,7 +3318,6 @@ import { freshStylesheetUrl, freshImageUrl } from './resources.js'; export default function VanillaProfileCard() { const ref = useRef(null); async function show() { - const quote = await fetchQuote(); const doc = ref.current.contentWindow.document; doc.open(); doc.write(` @@ -3279,17 +3327,34 @@ export default function VanillaProfileCard() { .profile-card img { border-radius: 50%; background: #dfe3e9; } .name { margin: 0 0 4px; font-family: 'Caveat', sans-serif; font-size: 22px; line-height: 28px; font-weight: bold; } .bio { margin: 0; font-family: 'Caveat', sans-serif; font-size: 20px; line-height: 26px; } + .avatar-placeholder { width: 80px; height: 80px; border-radius: 50%; background: #dfe3e9; } + .name-placeholder, .bio-placeholder { border-radius: 4px; background: #dfe3e9; color: transparent; } + .name-placeholder { width: 90px; } + .bio-placeholder { width: 220px; height: 52px; }
    - Jack Pope +
    -

    Jack Pope

    -

    ${quote}

    +

     

    +

     

    - `); doc.close(); + + const quote = await fetchQuote(); + doc.body.innerHTML = ` +
    + +
    +

    Jack Pope

    +

    ${quote}

    +
    +
    `; + const stylesheet = doc.createElement('link'); + stylesheet.rel = 'stylesheet'; + stylesheet.href = freshStylesheetUrl(); + doc.head.appendChild(stylesheet); } return ( <> @@ -3382,6 +3447,7 @@ hr { } .bio-placeholder { width: 220px; + height: 52px; } .vanilla-frame { display: block; @@ -3395,8 +3461,8 @@ hr { ```json package.json hidden { "dependencies": { - "react": "19.3.0-canary-f1f7ed2a-20260904", - "react-dom": "19.3.0-canary-f1f7ed2a-20260904", + "react": "19.3.0", + "react-dom": "19.3.0", "react-scripts": "latest" } } diff --git a/src/content/reference/react/ViewTransition.md b/src/content/reference/react/ViewTransition.md index 1011a1c96..17595bb76 100644 --- a/src/content/reference/react/ViewTransition.md +++ b/src/content/reference/react/ViewTransition.md @@ -1253,9 +1253,9 @@ It's important to properly use keys to preserve identity when reordering lists. ### Animating from Suspense content {/*animating-from-suspense-content*/} -Like any Transition, React waits for data and new CSS (``) before running the animation. In addition to this, ViewTransitions also wait up to 500ms for new fonts to load before starting the animation to avoid them flickering in later. For the same reason, an image wrapped in ViewTransition will wait for the image to load. See examples of [waiting for a font](/reference/react/Suspense#waiting-for-a-font-to-load) and [waiting for an image](/reference/react/Suspense#waiting-for-an-image-to-load) on the Suspense page. +Like any Transition, React waits for data and new CSS (``) before running the animation. `` also waits up to 500 ms for new fonts and visible images to load so they don't flicker in after the animation starts. See examples of [waiting for a font](/reference/react/Suspense#waiting-for-a-font-to-load) and [waiting for an image](/reference/react/Suspense#waiting-for-an-image-to-load) on the Suspense page. -If it's inside a new Suspense boundary instance, then the fallback is shown first. After the Suspense boundary fully loads, it triggers the `` to animate the reveal to the content. +If the content is inside a new Suspense boundary, React first shows the fallback. After the boundary finishes loading, `` animates the reveal to the content. There are two ways to animate Suspense boundaries depending on where you place the ``: @@ -1315,7 +1315,7 @@ export function VideoPlaceholder() { ``` ```js -import {ViewTransition, useState, startTransition, Suspense} from 'react'; +import { ViewTransition, Suspense, useState } from 'react'; import {Video, VideoPlaceholder} from './Video'; import {useLazyVideoData} from './data'; @@ -1328,12 +1328,7 @@ export default function Component() { const [showItem, setShowItem] = useState(false); return ( <> - {showItem ? ( @@ -1486,8 +1481,8 @@ button:hover { ```json package.json hidden { "dependencies": { - "react": "19.3.0-canary-f1f7ed2a-20260904", - "react-dom": "19.3.0-canary-f1f7ed2a-20260904", + "react": "19.3.0", + "react-dom": "19.3.0", "react-scripts": "latest" } } diff --git a/src/sidebarReference.json b/src/sidebarReference.json index 07b012ae3..e1ae1155f 100644 --- a/src/sidebarReference.json +++ b/src/sidebarReference.json @@ -410,6 +410,11 @@ "title": "React Performance tracks", "path": "/reference/dev-tools/react-performance-tracks" }, + { + "title": "React DevTools for agents", + "path": "/reference/dev-tools/react-devtools-cdt-mcp", + "version": "experimental" + }, { "hasSectionHeader": true, "sectionHeader": "eslint-plugin-react-hooks"