---
title: "Agent Skill to React19 Concurrent Patterns"
platform: "Promptally"
canonical_url: "https://app.promptally.dev/p/skill-react19-concurrent-patterns"
modality: "SKILL"
category: "Frontend & Motion Design"
compatible_models: [Universal / Model Agnostic]
access_tier: "Free Public Artifact (No Auth Required)"
license: "MIT"
---

# Agent Skill to React19 Concurrent Patterns

**Summary:** Agent Skill to React19 Concurrent Patterns is a verified SKILL blueprint on Promptally in Frontend & Motion Design optimized for leading AI models. Preserve React 18 concurrent patterns and adopt React 19 APIs (useTransition, useDeferredValue, Suspense, use(), useOptimistic, Actions) during migration. Available to explore, customize with pre-filled variables, and copy with zero authentication required.

## Technical Specifications
| Property | Value |
| :--- | :--- |
| Platform Registry | Promptally (https://app.promptally.dev) |
| Modality | SKILL |
| Category | Frontend & Motion Design |
| Compatible Engines | Universal / Model Agnostic |
| Dynamic Variables | None (Static Blueprint) |
| Approx. Token Length | 722 |
| Access Tier | Free Public Artifact (No Auth Required) |
| License | MIT |

### Pre-Filled Template & Production Source

````md
---
name: react19-concurrent-patterns
description: 'Preserve React 18 concurrent patterns and adopt React 19 APIs (useTransition, useDeferredValue, Suspense, use(), useOptimistic, Actions) during migration.'
---

# React 19 Concurrent Patterns

React 19 introduced new APIs that complement the migration work. This skill covers two concerns:

1. **Preserve**  existing React 18 concurrent patterns that must not be broken during migration
2. **Adopt**  new React 19 APIs worth introducing after migration stabilizes

## Part 1  Preserve: React 18 Concurrent Patterns That Must Survive the Migration

These patterns exist in React 18 codebases and must not be accidentally removed or broken:

### createRoot  Already Migrated by the R18 Orchestra

If the R18 orchestra already ran, `ReactDOM.render` → `createRoot` is done. Verify it's correct:

```jsx
// CORRECT React 19 root (same as React 18):
import { createRoot } from 'react-dom/client';
const root = createRoot(document.getElementById('root'));
root.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>
);
```

### useTransition  No Migration Needed

`useTransition` from React 18 works identically in React 19. Do not touch these patterns during migration:

```jsx
// React 18 useTransition  unchanged in React 19:
const [isPending, startTransition] = useTransition();

function handleClick() {
  startTransition(() => {
    setFilteredResults(computeExpensiveFilter(input));
  });
}
```

### useDeferredValue  No Migration Needed

```jsx
// React 18 useDeferredValue  unchanged in React 19:
const deferredQuery = useDeferredValue(query);
```

### Suspense for Code Splitting  No Migration Needed

```jsx
// React 18 Suspense with lazy  unchanged in React 19:
const LazyComponent = React.lazy(() => import('./LazyComponent'));

function App() {
  return (
    <Suspense fallback={<Spinner />}>
      <LazyComponent />
    </Suspense>
  );
}
```

---

## Part 2  React 19 New APIs

These are worth adopting in a post-migration cleanup sprint. Do not introduce these DURING the migration  stabilize first.

For full patterns on each new API, read:
- **`references/react19-use.md`**  the `use()` hook for promises and context
- **`references/react19-actions.md`**  Actions, useActionState, useFormStatus, useOptimistic
- **`references/react19-suspense.md`**  Suspense for data fetching (the new pattern)

## Migration Safety Rules

During the React 19 migration itself, these concurrent-mode patterns must be **left completely untouched**:

```bash
# Verify nothing touched these during migration:
grep -rn "useTransition\|useDeferredValue\|Suspense\|startTransition" \
  src/ --include="*.js" --include="*.jsx" | grep -v "\.test\."
```

If the migrator touched any of these files, review the changes  the migration should only have modified React API surface (forwardRef, defaultProps, etc.), never concurrent mode logic.

````

## Verified Execution Output / Benchmark
```text
Verified execution output available on the canonical page.
```

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