10 useEffect Best Practices

React’s useEffect hook is a powerful tool for managing side effects in your React components. It allows you to perform tasks such as fetching data, setting up subscriptions, and updating the DOM in response to user events.

However, useEffect can be tricky to use correctly. If you don’t use it properly, you can end up with bugs that are hard to track down. To help you avoid these issues, here are 10 best practices for using useEffect in your React components.

1. Avoid using useEffect in render

When you use useEffect in render, it will be called every time the component is rendered. This can lead to performance issues and unexpected behavior if not used correctly. It’s best practice to avoid using useEffect in render unless absolutely necessary.

Instead, try to move your logic into a separate function that can be called from within useEffect. This way, you can ensure that the code inside useEffect only runs when certain conditions are met, such as when props or state change.

2. Use the second argument of useEffect to control when it runs

The second argument of useEffect is an array of values that will be used to determine when the effect should run. If any of these values change, then the effect will run again. This allows you to control exactly when your effect runs and prevents it from running unnecessarily.

For example, if you have a component that fetches data from an API, you can pass in the URL as one of the values in the second argument. That way, whenever the URL changes, the effect will run again and fetch the new data. Without this second argument, the effect would run every time the component re-renders, which could lead to unnecessary network requests.

3. Avoid passing an empty array as a dependency

When you pass an empty array as a dependency, useEffect will only run once when the component mounts. This means that if any of the values in the array change, the effect won’t be re-run. This can lead to unexpected behavior and bugs in your application.

Instead, it’s best practice to include all variables that are used inside the effect as dependencies. That way, whenever one of those variables changes, the effect will be re-run with the updated value.

4. Don’t forget to cleanup your effects

When you use useEffect, React will remember the effect and run it again whenever a component re-renders. This can cause unexpected behavior if your effects are not properly cleaned up. For example, if you have an effect that sets a timer, but don’t clean it up when the component unmounts, then the timer will continue to run even after the component is gone.

To avoid this issue, always make sure to cleanup any effects you create in useEffect by returning a function from the callback. This function will be called when the component unmounts, allowing you to safely remove any timers or listeners you may have created.

5. Use useLayoutEffect for synchronous layout changes

useLayoutEffect runs synchronously after React has performed all DOM mutations. This means that the code inside useLayoutEffect will run before the browser paints, which is important for layout changes like measuring elements or animating them.

On the other hand, useEffect runs asynchronously and can cause a noticeable delay in rendering if it contains expensive operations. Therefore, it’s best to use useLayoutEffect when you need to make sure your layout changes are applied immediately.

6. Prefer useCallback over inline functions

When you use an inline function, React will create a new instance of the function every time it renders. This can cause unnecessary re-renders and performance issues if your component is rendering frequently.

On the other hand, when you use useCallback, React will only create a new instance of the function when one of its dependencies changes. This helps to ensure that your component isn’t unnecessarily re-rendering due to changes in the function itself.

7. Prefer useMemo over inline functions

When you use an inline function, React will create a new instance of the function every time it renders. This can lead to unnecessary re-renders and performance issues.

On the other hand, when you use useMemo, React will only create a new instance of the function if its dependencies have changed. This means that your component won’t be unnecessarily re-rendered, which can help improve performance. Additionally, using useMemo allows you to easily memoize values for better performance.

8. Consider splitting useEffects into multiple components

By splitting useEffect into multiple components, you can better control the order in which effects are executed. This is especially important when dealing with asynchronous operations such as API calls or data fetching.

By breaking up useEffect into smaller chunks, you can also make your code more readable and easier to debug. Additionally, it allows for greater flexibility when making changes to the codebase since each component can be modified independently of the others. Finally, it helps keep your application performant by ensuring that only necessary effects are run at any given time.

9. Be careful with infinite loops

When you use useEffect, it runs every time the component renders. If you have an infinite loop in your code, then the effect will run continuously and can cause performance issues or even crash the application. To avoid this, make sure to check for any conditions that could lead to an infinite loop before running the effect.

10. Make sure you’re not mutating state inside useEffect

When you mutate state inside useEffect, it can cause unexpected behavior and bugs. This is because the code in useEffect runs after every render, so if you’re mutating state inside of it, that mutation will be applied to the new state each time the component re-renders.

To avoid this issue, make sure you are not directly modifying state inside useEffect. Instead, create a copy of the state and modify that instead. Then, when you want to update the state, use the setState() method provided by React.