Alex Sidorenko

3 ways to cause an infinite loop in React

July 05, 2021

Have you spent some time trying to debug an infinite loop in React? Maybe you hung your browser a couple of times in the process. Or had one of these πŸ‘‡

Uncaught Error: Too many re-renders.
React limits the number of renders
to prevent an infinite loop.

Here are 3 potential causes of the infinite loop in React.

I. Updating the state inside the render

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

  setCount(1); // infinite loop

  return ...
}

If you update the state directly inside your render method or a body of a functional component, it will cause an infinite loop.

State updates β†’ triggers re-render β†’ state updates β†’ triggers re-render β†’ …

Fix πŸŽ‰

Do you want to update a state only one time when the component mounts? Use useEffect with an empty array as a dependency.

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

  useEffect(() => {
    setCount(1);
  }, [])
  

  return ...
}

II. Infinite loop in useEffect

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

  useEffect(() => {
    setCount(count + 1) // infinite loop
  }, [count])

  return ...
}

If you keep updating a state inside useEffect with a property you update set as a dependency, it will cause an infinite loop.

count updates β†’ useEffect detects updated dependency β†’ count updates β†’ useEffect detects updated dependency β†’ …

Fix πŸŽ‰

If you want to update a state based on its previous value, use a functional update. This way, you can remove state property from the dependency list and prevent an infinite loop.

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

  useEffect(() => {
    setCount(previousCount => previousCount + 1)
  }, [])

  return ...
}

III. Incorrectly set event handlers

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

  return (
    <button onClick={setCount(1)}>Submit</button> // infinite loop
  );
}

It is not the right way to set event handlers. You need to provide a function to the onClick, not the result of the function execution. By executing a function before setting a handler, you update a state inside the render, which causes an infinite loop.

State updates β†’ triggers re-render β†’ state updates β†’ triggers re-render β†’ …

Fix πŸŽ‰

Set a function to onClick event. It is a proper way to set event handlers. This way state will only update after a click of a button and won’t cause an infinite loop.

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

  return (
    <button onClick={() => setCount(1)}>Submit</button> // infinite loop
  );
}

How to spot infinite loops

Every time you update a state, picture the sequence of events that will happen after the update. If without additional user interaction, this sequence leads you back to the same state update, you probably have an infinite loop.

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