React 19.3 use() – The New Way to Handle Async Logic (and When It Beats useEffect)

React 19 introduced a new render-time API: use().

If you’ve ever felt that handling async data with useEffect + useState + “loading” + “error” flags is too much boilerplate, use() is basically React saying:

“What if you could just await a Promise directly inside your component?”

In this post, we’ll cover:

• What use() actually is (and why it’s not just another hook).
• How use() works with Promises and Context.
• Why and when to use use() instead of useEffect.
• The real benefits of use() vs useEffect, with simple code examples.

What is use() in React 19?

use() is a React render-time API that lets your component read the value of a resource, currently:

• A Promise (for async data)
• A Context (like ThemeContext, AuthContext, etc.)

import { use, Suspense } from "react";

function Message({ messagePromise }) {
  const message = use(messagePromise);      // read Promise
  const theme = use(ThemeContext);          // read Context

  return (
    <div style={{ color: theme.primaryColor }}>
      {message.text}
    </div>
  );
}

Key ideas:

• const value = use(resource);
• resource can be a Promise or a Context.
• use() must be called inside a component or a custom hook.
• Unlike regular hooks, use() can be called inside conditionals and loops.

How use() Works Under the Hood (Simple Mental Model)

When you call use(promise):

1. If the Promise is still pending
   • React suspends the component.
   • If the component is wrapped in <Suspense>, React shows the fallback UI.
2. When the Promise resolves
   • React re-renders the component.
   • This time, use(promise) returns the resolved value.
3. If the Promise rejects
   • React throws the error to the nearest Error Boundary, which can show a graceful error UI.

This tightly integrates use() with Suspense and Error Boundaries — you don’t manually manage isLoading or error state.

Example: Data Fetching Without useEffect

Old way: useEffect + useState

import { useEffect, useState } from "react";

function Weather() {
  const [weather, setWeather] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    let cancelled = false;

    async function load() {
      try {
        const res = await fetch("/api/weather");
        if (!cancelled) {
          const data = await res.json();
          setWeather(data);
        }
      } catch (e) {
        if (!cancelled) setError(e);
      } finally {
        if (!cancelled) setLoading(false);
      }
    }

    load();
    return () => {
      cancelled = true;
    };
  }, []);

  if (loading) return <p>Loading…</p>;
  if (error) return <p>Something went wrong.</p>;

  return <p>Current temperature: {weather.temp}°C</p>;
}

That’s a lot of boilerplate for something conceptually simple: “fetch data and render it”.

New way: use() + Suspense

Imagine you have a cached Promise (typically created in a Server Component or a loader):

// server / loader code (simplified)
export function getWeather() {
  return fetch("/api/weather").then((res) => res.json());
}

Now use it in a component:

import { use, Suspense } from "react";
import { getWeather } from "./weatherApi";

const weatherPromise = getWeather(); // ideally created/cached at a higher level

function Weather() {
  const weather = use(weatherPromise);

  return <p>Current temperature: {weather.temp}°C</p>;
}

export default function WeatherSection() {
  return (
    <Suspense fallback={<p>Loading weather…</p>}>
      <Weather />
    </Suspense>
  );
}

What changed?

• No useEffect.
• No useState.
• No manual loading / error flags.
• Suspense handles loading UI.
• Error Boundary can handle failures.

Cleaner, more declarative and easier to follow.

Using use() with Context

use() can also read from a Context directly:

import { createContext, use } from "react";

const ThemeContext = createContext(null);

function ThemedButton() {
  const theme = use(ThemeContext);

  return (
    <button style={{ background: theme.bg, color: theme.fg }}>
      Click me
    </button>
  );
}

This is mostly ergonomic sugar over useContext(ThemeContext) — but it’s powerful because the same use() works for both Promises and Context, and it can be used inside conditionals and loops.

Why Use use()? (Practical Benefits)

1. Less Boilerplate for Async Data

With useEffect, you usually need:

• useState for data.
• useState for loading/error.
• Cleanup logic.
• Edge cases (component unmount, race conditions).

With use():

• You just read the Promise.
• Suspense + Error Boundaries deal with loading and error UI.

👉 Result: Fewer lines of code, fewer moving parts, fewer bugs

2. More Declarative, “Synchronous”-Feeling Code

use() lets your React code read like normal await logic:

const weather = use(weatherPromise);
// immediately use `weather`

Your component describes what it needs, not how to orchestrate the async steps.

3. Works Inside Conditionals and Loops

This is a big change from regular hooks.

You cannot do this with useEffect or other Hooks:

//  invalid
if (someCondition) {
  const data = useEffect(...);
}

But with use() you can:

function Post({ showAuthor, postPromise, authorPromise }) {
  const post = use(postPromise);

  let authorInfo = null;
  if (showAuthor) {
    const author = use(authorPromise); // 
    authorInfo = <p>By {author.name}</p>;
  }

  return (
    <article>
      <h1>{post.title}</h1>
      {authorInfo}
    </article>
  );
}

use() isn’t a “stateful hook” that depends on call order like useState or useEffect, so it doesn’t follow the same Rules of Hooks. That’s why it’s allowed in conditionals and loops.

4. Built-in Suspense and Error Handling

use() is designed to work with:

• <Suspense> for loading states.
• Error Boundaries for failures.

You architect your UI in boundaries, and use() plugs into that naturally. No more repeating the same loading / error template across components.

use() vs useEffect: When to Use What

When use() is better than useEffect

Use use() when:

• You want to read async data (Promises) during render.
• You’re already using React 19 with Suspense boundaries.
• The Promise is created and cached at a higher level (often in Server Components / loaders).
• You want declarative data fetching without useState/useEffect boilerplate.

Typical use cases:

• Page or section data loading.
• Reading data returned from a Server Action.
• Streaming data from server to client in modern frameworks (Next.js, Remix, React Router v7).

When useEffect is still the right choice

use() does not kill useEffect. You still need useEffect for imperative side effects, such as:

• Subscribing/unsubscribing to WebSockets or event listeners.
• Managing timers (setInterval, setTimeout).
• Direct DOM manipulation or integration with non-React UI libraries.
• Analytics, logging, or any effect that should run after paint.

Example that still needs useEffect:

import { useEffect } from "react";

function OnlineStatusIndicator() {
  useEffect(() => {
    function handleOnline() {
      console.log("User is online");
    }
    window.addEventListener("online", handleOnline);
    return () => {
      window.removeEventListener("online", handleOnline);
    };
  }, []);

  return <span>●</span>;
}

Rule of thumb:

• Reading data? → Prefer use() (with Suspense).
• Causing side effects (subscriptions, timers, DOM, logging)? → Use useEffect.

Best Practices for Using use() in Real Apps

1. Cache Promises
   Don’t create a new Promise on every render. Create it in a Server Component, loader, or module scope, then pass it down.
2. Wrap components in <Suspense>
   Any component calling use(promise) should have a Suspense boundary above it with a meaningful fallback.
3. Use Error Boundaries
   Pair use() + Suspense with Error Boundaries for a clean error UX.
4. Don’t use use() for everything
   Continue to use useEffect for non-data side effects. use() is about reading values, not causing effects.
5. Keep components small and focused
   Since use() can appear in conditionals and loops, keep components easy to reason about — small, focused pieces instead of giant “god components”.

Quick Summary: use() vs useEffect

Conclusion

React 19.3’s use() marks a big shift in how we think about async data in React:

• Data fetching becomes cleaner and more declarative.
• You write less boilerplate compared to useEffect + useState.
• Suspense and Error Boundaries become central to your UX, not afterthoughts.

Don’t think of use() as a replacement for useEffect, but as a new tool:

• Use use() to read async resources during render.
• Use useEffect to perform side effects after render.

If you’re already setting up React 19 in your project, start small: migrate one data-loading component from useEffect to use() with Suspense, and you’ll immediately feel the difference.

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