vercel-react-view-transitions

# React View Transitions

Animate between UI states using the browser's native `document.startViewTransition`. Declare *what* with `<ViewTransition>`, trigger *when* with `startTransition` / `useDeferredValue` / `Suspense`, control *how* with CSS classes. Unsupported browsers skip animations gracefully.

## When to Animate

Every `<ViewTransition>` should communicate a spatial relationship or continuity. If you can't articulate what it communicates, don't add it.

Implement **all** applicable patterns from this list, in this order:

| Priority | Pattern | What it communicates |
|----------|---------|---------------------|
| 1 | **Shared element** (`name`) | "Same thing — going deeper" |
| 2 | **Suspense reveal** | "Data loaded" |
| 3 | **List identity** (per-item `key`) | "Same items, new arrangement" |
| 4 | **State change** (`enter`/`exit`) | "Something appeared/disappeared" |
| 5 | **Route change** (layout-level) | "Going to a new place" |

This is an implementation order, not a "pick one" list. Implement every pattern that fits the app. Only skip a pattern if the app has no use case for it.

### Choosing Animation Style

| Context | Animation | Why |
|---------|-----------|-----|
| Hierarchical navigation (list → detail) | Type-keyed `nav-forward` / `nav-back` | Communicates spatial depth |
| Lateral navigation (tab-to-tab) | Bare `<ViewTransition>` (fade) or `default="none"` | No depth to communicate |
| Suspense reveal | `enter`/`exit` string props | Content arriving |
| Revalidation / background refresh | `default="none"` | Silent — no animation needed |

Reserve directional slides for hierarchical navigation (list → detail) and ordered sequences (prev/next photo, carousel, paginated results). For ordered sequences, the direction communicates position: "next" slides from right, "previous" from left. Lateral/unordered navigation (tab-to-tab) should not use directional slides — it falsely implies spatial depth.

---

## Availability

- **Next.js:** Do **not** install `react@canary` — the App Router already bundles React canary internally. `ViewTransition` works out of the box. `npm ls react` may show a stable-looking version; this is expected.
- **Without Next.js:** Install `react@canary react-dom@canary` (`ViewTransition` is not in stable React).
- Browser support: Chromium 111+, Firefox 144+, Safari 18.2+. Graceful degradation on unsupported browsers.

---

## Implementation Workflow

When adding view transitions to an existing app, **follow `references/implementation.md` step by step.** Start with the audit — do not skip it. Copy the CSS recipes from `references/css-recipes.md` into the global stylesheet — do not write your own animation CSS.

---

## Core Concepts

### The `<ViewTransition>` Component

```jsx
import { ViewTransition } from 'react';

<ViewTransition>
  <Component />
</ViewTransition>
```

React auto-assigns a unique `view-transition-name` and calls `document.startViewTransition` behind the scenes. Never call `startViewTransition` yourself.

### Animation Triggers

| Trigger | When it fires |
|---------|--------------|
| **enter** | `<ViewTransition>` first inserted during a Transition |
| **exit** | `<ViewTransition>` first removed during a Transition |
| **update** | DOM mutations inside a `<ViewTransition>`. With nested VTs, mutation applies to the innermost one |
| **share** | Named VT unmounts and another with same `name` mounts in the same Transition |

Only `startTransition`, `useDeferredValue`, or `Suspense` activate VTs. Regular `setState` does not animate.

### Critical Placement Rule

`<ViewTransition>` only activates enter/exit if it appears **before any DOM nodes**:

```jsx
// Works
<ViewTransition enter="auto" exit="auto">
  <div>Content</div>
</ViewTransition>

// Broken — div wraps the VT, suppressing enter/exit
<div>
  <ViewTransition enter="auto" exit="auto">
    <div>Content</div>
  </ViewTransition>
</div>
```

---

## Styling with View Transition Classes

### Props

Values: `"auto"` (browser cross-fade), `"none"` (disabled), `"class-name"` (custom CSS), or `{ [type]: value }` for type-specific animations.

```jsx
<ViewTransition default="none" enter="slide-in" exit="slide-out" share="morph" />
```

If `default` is `"none"`, all triggers are off unless explicitly listed.

### CSS Pseudo-Elements

- `::view-transition-old(.class)` — outgoing snapshot
- `::view-transition-new(.class)` — incoming snapshot
- `::view-transition-group(.class)` — container
- `::view-transition-image-pair(.class)` — old + new pair

See `references/css-recipes.md` for ready-to-use animation recipes.

---

## Transition Types

Tag transitions with `addTransitionType` so VTs can pick different animations based on context. Call it multiple times to stack types — different VTs in the tree react to different types:

```jsx
startTransition(() => {
  addTransitionType('nav-forward');
  addTransitionType('select-item');
  router.push('/detail/1');
});
```

Pass an object to map types to CSS classes. Works on `enter`, `exit`, **and** `share`:

```jsx
<ViewTransition
  enter={{ 'nav-forward': 'slide-from-right', 'nav-back': 'slide-from-left', default: 'none' }}
  exit={{ 'nav-forward': 'slide-to-left', 'nav-back': 'slide-to-right', default: 'none' }}
  share={{ 'nav-forward': 'morph-forward', 'nav-back': 'morph-back', default: 'morph' }}
  default="none"
>
  <Page />
</ViewTransition>
```

`enter` and `exit` don't have to be symmetric. For example, fade in but slide out directionally:

```jsx
<ViewTransition
  enter={{ 'nav-forward': 'fade-in', 'nav-back': 'fade-in', default: 'none' }}
  exit={{ 'nav-forward': 'nav-forward', 'nav-back': 'nav-back', default: 'none' }}
  default="none"
>
```

**TypeScript:** `ViewTransitionClassPerType` requires a `default` key in the object.

For apps with multiple pages, extract the type-keyed VT into a reusable wrapper:

```jsx
export function DirectionalTransition({ children }: { children: React.ReactNode }) {
  return (
    <ViewTransition