React Hook 'useState' is called conditionally error

React Hook 'useState' is called conditionally error #

The error "React hook 'useState' is called conditionally" occurs when we use the useState hook conditionally or after a condition that may return a value. To solve the error, move all React hooks above any conditionals that may return a value.

react hook usestate called conditionally

Here is an example of how the error occurs.

App.js

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import React, {useState} from 'react';

export default function App() {
  const [count, setCount] = useState(0);

  if (count > 0) {
    return <h1>Count is greater than 0</h1>;
  }

  // ⛔️ React Hook "useState" is called conditionally.
  //React Hooks must be called in the exact same order
  // in every component render. Did you accidentally call
  // a React Hook after an early return?
  const [message, setMessage] = useState('');

  return (
    <div>
      <h2>Count: {count}</h2>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

The issue in the code snippet is - we use the second useState hook after a condition that may return a value.

To solve the error, we must only call React hooks at the top level.

App.js

Copied!
import React, {useState} from 'react';

export default function App() {
  const [count, setCount] = useState(0);

  // 👇️ move hooks above condition that might return
  const [message, setMessage] = useState('');

  // 👇️ any conditions that might return must be below all hooks
  if (count > 0) {
    return <h1>Count is greater than 0</h1>;
  }

  return (
    <div>
      <h2>Count: {count}</h2>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

We moved the second useState hook above the condition that might return a value.

This solves the error because we have to ensure that React hooks are called in the same order each time a component renders.

This means that we aren't allowed to use hooks inside loops, conditions or nested functions.

We should never call a hook conditionally.

App.js

Copied!
import React, {useState} from 'react';

export default function App() {
  const [count, setCount] = useState(0);

  if (count === 0) {
    // ⛔️ React Hook "useState" is called conditionally.
    // React Hooks must be called in the exact same order in every component render.
    const [message, setMessage] = useState('');
  }


  return (
    <div>
      <h2>Count: {count}</h2>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

The code snippet above causes the error because we are calling the second useState hook conditionally.

This is not allowed because the number of hooks and the order of hook calls have to be the same on re-renders of our function components.

To solve the error, we have to move the useState call to the top level and not conditionally call the hook.

Like the documentation states:

Only call hooks at the top level
Don't call hooks inside loops, conditions or nested functions
Always use hooks at the top level of your React function, before any early returns
Only call hooks from React function components or from custom hooks.

This helps React preserve the state of hooks between multiple useState calls.

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React Hook 'useState' is called conditionally error

React Hook 'useState' is called conditionally error #

Conclusion #

Borislav Hadzhiev