Prevent Multiple Renders in React | React Component Rendering Twice
Does your React component render twice? I have a simple app that has state containing a number. We are using useState and useEffect. In useEffect we added an eventlistener on window object. When we click at document, it updates state and logs in console. When component loads first time, it renders twice because it is logging in console twice what i have used in useEffect. So why useEffect is running twice on component load?
In React, there is a thing called StrictMode. React StrictMode renders component twice on development environment but not in production. This is to detect any problems with your code. useEffect itself will only be called once.
If you have StrictMode enabled in your app, it might be because you used create-react-app or similar to create your app initially, which automatically enables StrictMode by default. You can find your app wrapped by React.StrictMode in your index.js file
If you want to disable strict mode, you can comment these lines or remove React StrictMode tag. But I would suggest to leave it as is because it will help you catch bugs. If you go to ReactJS docs, you will find strict mode information.
Strict Mode does not render any visibble UI in React, just like Fragment. It activates additional checks and warnings for its descendants. Instead of enabling it for whole application, you can also enable strict mode for any part of your application.
According to official docs, React Strict mode helps with:
- Identifying components with unsafe lifecycles
- Warning about legacy string ref API usage
- Warning about deprecated findDOMNode usage
- Detecting unexpected side effects
- Detecting legacy context API
- Ensuring reusable state
There can be other causes for multiple renders too. For example:
- If concerned component appears more than once in your page
- If something higher up the tree is unmounting and remounting
Then also you may see multiple renders in React. So check for that as well. But first check for React Strict Mode if its on.
In this video we covered following:
- React Hook useEffect called twice even if an empty array is used as an argument
- useEffect runs twice
- React component rendering twice
- React calling a function twice
- Multiple renders in React
- React useEffect executing twice on page load
- useEffect is called twice
- React useEffect making multiple requests
- useEffect calls function twice
- React component mounting twice
- React component rendering twice
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