Using the use() Hook in React 19

Teaches when and how to use React 19's new use() API: reads Promises (suspending component) and Context (conditionally—inside if statements, loops, after early returns).

Activates when: User mentions use(), use hook, async patterns, Suspense + data fetching, conditional context, or useContext migration.

Key Capabilities vs. Traditional Hooks

Usage Patterns

Reading Promises:

import { use, Suspense } from 'react';

async function fetchUser(id) {
  const res = await fetch(`/api/users/${id}`);
  return res.json();
}

function UserProfile({ userId }) {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <UserData promise={fetchUser(userId)} />
    </Suspense>
  );
}

function UserData({ promise }) {
  const user = use(promise);
  return <div>{user.name}</div>;
}

Conditional Context Access:

import { use, createContext } from 'react';

const ThemeContext = createContext('light');

function Button({ isPrimary, children }) {
  let className = 'button';
  if (isPrimary) {
    const theme = use(ThemeContext);
    className += ` ${theme}`;
  }
  return <button className={className}>{children}</button>;
}

Reusable Custom Hook:

import { use, cache } from 'react';

const getUser = cache(async (id) => {
  const res = await fetch(`/api/users/${id}`);
  return res.json();
});

function useUser(userId) {
  if (!userId) return null;
  return use(getUser(userId));
}

Implementation Workflow

Async data: Pass Promise as prop from parent → wrap component in Suspense boundary → use use(promise) in child → catch errors with Error Boundary.

Conditional context: Replace useContext(Context) with use(Context) for flexibility across conditional branches, loops, post-early-return.

Migration from useContext: Find useContext(Context) calls → replace with use(Context) → benefits: now conditional if needed.

Requirements & Validation

MUST:

• Wrap use(promise) in Suspense boundary with fallback
• Use Error Boundary (not try-catch) for error handling
• Create Promises in parents/Server Components, pass as props
• Use cache() wrapper to prevent duplicate requests

NEVER:

• Call use() inside try-catch blocks
• Create new Promises inside component (causes infinite loops)
• Use use() outside Component/Hook functions
• Omit Suspense boundary for Promises

Verify:

1. Suspense boundary wraps every use(promise) with fallback
2. Error Boundary catches Promise errors
3. Promises created externally or with cache()—stable across renders
4. All conditional logic branches tested

For comprehensive React 19 use() documentation:

research/react-19-comprehensive.md lines 241–311 (use API, Promise Patterns, useContext sections).