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Async Functions in React useEffect

Posted by Ryan Neilson on in Dev Tips, React

When using React’s useEffect hook we may want to write an asynchronous function, perhaps to fetch some data. There are some important considerations when combining async with useEffect, discussed further below.

Don’t Do This

The wrong way to write an async function with useEffect looks something like this:

// DON'T DO THIS
useEffect(async () => {
  const data = await fetch('https://someapi.com');
}, [])

The main problem with the code above is that the first argument of useEffect should be a function that returns a function or nothing at all. Using an async function we return a Promise, which can’t be called as a function. This can lead to unexpected results, including errors where we attempt to access an unmounted component.

Do This Instead

We can instead write our asynchronous code inside the useEffect hook like this:

useEffect(() => {
  const fetchData = async () => {
    const data = await fetch('https://someapi.com');
  }

  fetchData();
}, [])

This is the most stripped down version of how to pair asynchronous code with the useEffect hook. In practice it’s a good idea to implement error handling and cleanup functions where applicable.

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Ryan Neilson is a software developer from Nova Scotia, Canada, where he lives with his wife and their menagerie of pets. He has worked extensively with PHP, WordPress, JavaScript, React, SCSS and CSS. Ryan can be found professionally at News Corp, where he works as a lead software engineer.

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