Double Component Loads in React with React RouterDouble Component Loads in React with React RouterDouble Component Loads in React with React Router

The Problem

Recently, I encountered a perplexing issue while working with React Router in my React application — my components were loading twice every time I navigated to a new route. This behavior was puzzling and seemed to defy the expected behavior of a single component mount per route change. After some investigation and troubleshooting, I've resolved the issue and wanted to share my findings with the community.

The Usual Suspects

ChatGPT told me that there are several reasons why components might load more than once in React. I've listed them below for reference:

1. Incorrect Route Configuration: Overlapping paths or improperly nested routes can lead to multiple component mounts.
2. StrictMode: React's StrictMode can lead to intentional double invocation of certain lifecycle methods in development mode to help detect side effects.
3. Multiple Router Instances: Using more than one <BrowserRouter> or <Router> instance can reset router state and cause re-mounts.
4. Code Splitting and Lazy Loading: Components may re-render due to state changes if React.lazy and Suspense are used for code splitting and lazy loading.
5. Misuse of the key Prop: Incorrect use of the key prop on route components can trigger re-mounts on route changes.
6. State Management Issues: Misconfigurations with state management libraries like Redux or MobX can lead to multiple renders.
7. Hot Reloading: During development, module updates with hot reloading can cause components to reload.

Resolving the Issue

To resolve the issue, you can take the following steps:

• Confirm that your route configuration is correct and contains no duplicates.
• Understand that StrictMode will cause additional renders only in development and verify that this is the behavior you're observing.
• Ensure you're using only one instance of <Router> in your application.
• If using code splitting, check that React.lazy and Suspense are implemented correctly and not causing unnecessary re-renders.
• Review your use of the key prop to make sure it's not causing components to remount unnecessarily on route changes.

The Culprit: React.StrictMode

In my case, the culprit was React.StrictMode. This tool is designed for detecting potential issues, but it has a side effect of double rendering components to identify problems with your code that will not adhere to the strict mode policies.

Here's what you need to know about StrictMode:

• It only affects the development build, not the production build.
• It helps identify components with unsafe lifecycles, legacy string ref API usage, deprecated findDOMNode usage, and unexpected side effects.
• It intentionally doubles the invocation of the following functions: constructor, render, shouldComponentUpdate, and the various lifecycle methods.

I just removed StrictMode from my application and the double rendering stopped.

Conclusion

After identifying StrictMode as the reason for the double loading of my components, I decided to keep it in place during development to benefit from its checks and warnings. However, it's important to remember that this behavior won't occur in a production build, so there's no impact on end-users.

I hope this exploration helps others who might be facing similar issues. Remember, tools like React.StrictMode are there to assist us, but knowing when and how they affect your development process is key to using them effectively.

Happy coding!