react18-use

React 19 use hook shim

Motivation

While waiting for React 19, I still want to release a library that depends on React 19 use hook. Hense, this shim.

It also provides useMemo + use(Context) experimental feature, which we hope to have in React 19. (See: https://x.com/TkDodo/status/1741193371283026422 )

Install

npm install react18-use

Usage

Promise

It works both in React 18 and React 19. However, you don't need it if you are using React 19.

import { Suspense, useState } from 'react';
import { use } from 'react18-use';

const Counter = ({ countPromise }: { countPromise: Promise<number> }) => {
  const count = use(countPromise);
  return <p>Count: {count}</p>;
};

const App = () => {
  const [countPromise, setCountPromise] = useState(Promise.resolve(0));
  return (
    <div>
      <button
        onClick={() =>
          setCountPromise(async (prev) => {
            await new Promise((resolve) => setTimeout(resolve, 1000));
            return (await prev) + 1;
          })
        }
      >
        +1
      </button>
      <Suspense fallback={<p>Loading...</p>}>
        <Counter countPromise={countPromise} />
      </Suspense>
    </div>
  );
};

Context

It works both in React 18 and React 19.

import { useState } from 'react';
import type { ReactNode } from 'react';
import { createContext, use, useMemo } from 'react18-use';

const MyContext = createContext({ foo: '', count: 0 });

const Component = () => {
  const foo = useMemo(() => {
    const { foo } = use(MyContext);
    return foo;
  }, []);
  return (
    <p>
      Foo: {foo} ({Math.random()})
    </p>
  );
};

const MyProvider = ({ children }: { children: ReactNode }) => {
  const [count, setCount] = useState(1);
  return (
    <div>
      <button onClick={() => setCount((c) => c + 1)}>{count}</button>
      <MyContext.Provider value={{ foo: 'React', count }}>
        {children}
      </MyContext.Provider>
    </div>
  );
};

const App = () => (
  <MyProvider>
    <Component />
  </MyProvider>
);

Limitations

• Only supports promises and contexts.
• It might not work exactly the same as React 19.
• useMemo with use(Context) is experimental (feedback welcome).

Examples

The examples folder contains working examples. You can run one of them with

PORT=8080 pnpm run examples:01_counter

and open http://localhost:8080 in your web browser.

You can also try them directly: 01 02

Tweets

• https://x.com/dai_shi/status/1823896762542928373
• https://x.com/dai_shi/status/1824424680721354980
• https://x.com/dai_shi/status/1825484689030955094