useEffectEvent

const onEvent = useEffectEvent(callback)

• Reference
  • useEffectEvent(callback)
• Usage
  • Using an event in an Effect
  • Using a timer with latest values
  • Using an event listener with latest values
  • Avoid reconnecting to external systems
  • Using Effect Events in custom Hooks
• Troubleshooting
  • I’m getting an error: “A function wrapped in useEffectEvent can’t be called during rendering”
  • I’m getting a lint error: “Functions returned from useEffectEvent must not be included in the dependency array”
  • I’m getting a lint error: ”… is a function created with useEffectEvent, and can only be called from Effects”

Reference

useEffectEvent(callback)

Call useEffectEvent at the top level of your component to create an Effect Event.

import { useEffectEvent, useEffect } from 'react';

function ChatRoom({ roomId, theme }) {
  const onConnected = useEffectEvent(() => {
    showNotification('Connected!', theme);
  });
}

Effect Events are a part of your Effect logic, but they behave more like an event handler. They always “see” the latest values from render (like props and state) without re-synchronizing your Effect, so they’re excluded from Effect dependencies. See Separating Events from Effects to learn more.

See more examples below.

Parameters

• callback: A function containing the logic for your Effect Event. The function can accept any number of arguments and return any value. When you call the returned Effect Event function, the callback always accesses the latest committed values from render at the time of the call.

Returns

useEffectEvent returns an Effect Event function with the same type signature as your callback.

You can call this function inside useEffect, useLayoutEffect, useInsertionEffect, or from within other Effect Events in the same component.

Caveats

• useEffectEvent is a Hook, so you can only call it at the top level of your component or your own Hooks. You can’t call it inside loops or conditions. If you need that, extract a new component and move the Effect Event into it.
• Effect Events can only be called from inside Effects or other Effect Events. Do not call them during rendering or pass them to other components or Hooks. The eslint-plugin-react-hooks linter enforces this restriction.
• Do not use useEffectEvent to avoid specifying dependencies in your Effect’s dependency array. This hides bugs and makes your code harder to understand. Only use it for logic that is genuinely an event fired from Effects.
• Effect Event functions do not have a stable identity. Their identity intentionally changes on every render.

// 🔴 Wrong: including Effect Event in dependencies
useEffect(() => {
  onSomething();
}, [onSomething]); // ESLint will warn about this

Usage

Using an event in an Effect

Call useEffectEvent at the top level of your component to create an Effect Event:

const onConnected = useEffectEvent(() => {
  if (!muted) {
    showNotification('Connected!');
  }
});

useEffectEvent accepts an event callback and returns an Effect Event. The Effect Event is a function that can be called inside of Effects without re-connecting the Effect:

useEffect(() => {
  const connection = createConnection(roomId);
  connection.on('connected', onConnected);
  connection.connect();
  return () => {
    connection.disconnect();
  }
}, [roomId]);

Since onConnected is an Effect Event, muted and onConnect are not in the Effect dependencies.

// 🔴 Wrong: Using Effect Events to hide dependencies
const logVisit = useEffectEvent(() => {
  log(pageUrl);
});

useEffect(() => {
  logVisit()
}, []); // Missing pageUrl means you miss logs

Using a timer with latest values

When you use setInterval or setTimeout in an Effect, you often want to read the latest values from render without restarting the timer whenever those values change.

This counter increments count by the current increment value every second. The onTick Effect Event reads the latest count and increment without causing the interval to restart:

Try changing the increment value while the timer is running. The counter immediately uses the new increment value, but the timer keeps ticking smoothly without restarting.

Using an event listener with latest values

When you set up an event listener in an Effect, you often need to read the latest values from render in the callback. Without useEffectEvent, you would need to include the values in your dependencies, causing the listener to be removed and re-added on every change.

This example shows a dot that follows the cursor, but only when “Can move” is checked. The onMove Effect Event always reads the latest canMove value without re-running the Effect:

Toggle the checkbox and move your cursor. The dot responds immediately to the checkbox state, but the event listener is only set up once when the component mounts.

Avoid reconnecting to external systems

A common use case for useEffectEvent is when you want to do something in response to an Effect, but that “something” depends on a value you don’t want to react to.

In this example, a chat component connects to a room and shows a notification when connected. The user can mute notifications with a checkbox. However, you don’t want to reconnect to the chat room every time the user changes the settings:

Try switching rooms. The chat reconnects and shows a notification. Now mute the notifications. Since muted is read inside the Effect Event rather than the Effect, the chat stays connected.

Using Effect Events in custom Hooks

You can use useEffectEvent inside your own custom Hooks. This lets you create reusable Hooks that encapsulate Effects while keeping some values non-reactive:

In this example, useInterval is a custom Hook that sets up an interval. The callback passed to it is wrapped in an Effect Event, so the interval does not reset even if a new callback is passed in every render.

Troubleshooting

I’m getting an error: “A function wrapped in useEffectEvent can’t be called during rendering”

This error means you’re calling an Effect Event function during the render phase of your component. Effect Events can only be called from inside Effects or other Effect Events.

function MyComponent({ data }) {
  const onLog = useEffectEvent(() => {
    console.log(data);
  });

  // 🔴 Wrong: calling during render
  onLog();

  // ✅ Correct: call from an Effect
  useEffect(() => {
    onLog();
  }, []);

  return <div>{data}</div>;
}

If you need to run logic during render, don’t wrap it in useEffectEvent. Call the logic directly or move it into an Effect.

I’m getting a lint error: “Functions returned from useEffectEvent must not be included in the dependency array”

If you see a warning like “Functions returned from useEffectEvent must not be included in the dependency array”, remove the Effect Event from your dependencies:

const onSomething = useEffectEvent(() => {
  // ...
});

// 🔴 Wrong: Effect Event in dependencies
useEffect(() => {
  onSomething();
}, [onSomething]);

// ✅ Correct: no Effect Event in dependencies
useEffect(() => {
  onSomething();
}, []);

Effect Events are designed to be called from Effects without being listed as dependencies. The linter enforces this because the function identity is intentionally not stable. Including it would cause your Effect to re-run on every render.

I’m getting a lint error: ”… is a function created with useEffectEvent, and can only be called from Effects”

If you see a warning like ”… is a function created with React Hook useEffectEvent, and can only be called from Effects and Effect Events”, you’re calling the function from the wrong place:

const onSomething = useEffectEvent(() => {
  console.log(value);
});

// 🔴 Wrong: calling from event handler
function handleClick() {
  onSomething();
}

// 🔴 Wrong: passing to child component
return <Child onSomething={onSomething} />;

// ✅ Correct: calling from Effect
useEffect(() => {
  onSomething();
}, []);

Effect Events are specifically designed to be used in Effects local to the component they’re defined in. If you need a callback for event handlers or to pass to children, use a regular function or useCallback instead.