react.dev/content/warnings/invalid-hook-call-warning.md

---
title: Invalid Hook Call Warning
layout: single
permalink: warnings/invalid-hook-call-warning.html
---

 You are probably here because you got the following error message:

 > Hooks can only be called inside the body of a function component.

There are three common reasons you might be seeing it:

1. You might have **mismatching versions** of React and React DOM.
2. You might be **breaking the [Rules of Hooks](/docs/hooks-rules.html)**.
3. You might have **more than one copy of React** in the same app.

Let's look at each of these cases.

## Mismatching Versions of React and React DOM

You might be using a version of `react-dom` (< 16.8.0) or `react-native` (< 0.60) that doesn't yet support Hooks. You can run `npm ls react-dom` or `npm ls react-native` in your application folder to check which version you're using. If you find more than one of them, this might also create problems (more on that below).

## Breaking the Rules of Hooks

You can only call Hooks **while React is rendering a function component**:

* ✅ Call them at the top level in the body of a function component.
* ✅ Call them at the top level in the body of a [custom Hook](/docs/hooks-custom.html).

**Learn more about this in the [Rules of Hooks](/docs/hooks-rules.html).**

```js{2-3,8-9}
function Counter() {
  // ✅ Good: top-level in a function component
  const [count, setCount] = useState(0);
  // ...
}

function useWindowWidth() {
  // ✅ Good: top-level in a custom Hook
  const [width, setWidth] = useState(window.innerWidth);
  // ...
}
```

To avoid confusion, it’s **not** supported to call Hooks in other cases:

* 🔴 Do not call Hooks in class components.
* 🔴 Do not call in event handlers.
* 🔴 Do not call Hooks inside functions passed to `useMemo`, `useReducer`, or `useEffect`.

If you break these rules, you might see this error.

```js{3-4,11-12,20-21}
function Bad1() {
  function handleClick() {
    // 🔴 Bad: inside an event handler (to fix, move it outside!)
    const theme = useContext(ThemeContext);
  }
  // ...
}

function Bad2() {
  const style = useMemo(() => {
    // 🔴 Bad: inside useMemo (to fix, move it outside!)
    const theme = useContext(ThemeContext);
    return createStyle(theme);
  });
  // ...
}

class Bad3 extends React.Component {
  render() {
    // 🔴 Bad: inside a class component
    useEffect(() => {})
    // ...
  }
}
```

You can use the [`eslint-plugin-react-hooks` plugin](https://www.npmjs.com/package/eslint-plugin-react-hooks) to catch some of these mistakes.

>Note
>
>[Custom Hooks](/docs/hooks-custom.html) *may* call other Hooks (that's their whole purpose). This works because custom Hooks are also supposed to only be called while a function component is rendering.


## Duplicate React

In order for Hooks to work, the `react` import from your application code needs to resolve to the same module as the `react` import from inside the `react-dom` package.

If these `react` imports resolve to two different exports objects, you will see this warning. This may happen if you **accidentally end up with two copies** of the `react` package.

If you use Node for package management, you can run this check in your project folder:

    npm ls react

If you see more than one React, you'll need to figure out why this happens and fix your dependency tree. For example, maybe a library you're using incorrectly specifies `react` as a dependency (rather than a peer dependency). Until that library is fixed, [Yarn resolutions](https://yarnpkg.com/lang/en/docs/selective-version-resolutions/) is one possible workaround.

You can also try to debug this problem by adding some logs and restarting your development server:

```js
// Add this in node_modules/react-dom/index.js
window.React1 = require('react');

// Add this in your component file
require('react-dom');
window.React2 = require('react');
console.log(window.React1 === window.React2);
```

If it prints `false` then you might have two Reacts and need to figure out why that happened. [This issue](https://github.com/facebook/react/issues/13991) includes some common reasons encountered by the community.

This problem can also come up when you use `npm link` or an equivalent. In that case, your bundler might "see" two Reacts — one in application folder and one in your library folder. Assuming `myapp` and `mylib` are sibling folders, one possible fix is to run `npm link ../myapp/node_modules/react` from `mylib`. This should make the library use the application's React copy.

>Note
>
>In general, React supports using multiple independent copies on one page (for example, if an app and a third-party widget both use it). It only breaks if `require('react')` resolves differently between the component and the `react-dom` copy it was rendered with.

## Other Causes

If none of this worked, please comment in [this issue](https://github.com/facebook/react/issues/13991) and we'll try to help. Try to create a small reproducing example — you might discover the problem as you're doing it.