How to Resolve ReactDOM.render is No Longer Supported Warning in React 18 Testing?

Learn how to resolve the 'ReactDOM.render is no longer supported' warning in React 18 when writing tests with React Testing Library and React hooks.
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How to Resolve ReactDOM.render is No Longer Supported Warning in React 18 Testing?

With the release of React 18, developers need to navigate through various updates and changes, one of the notable ones being the deprecation of ReactDOM.render. This change affects not just application code but also testing environments. Here's how you can resolve the ReactDOM.render is no longer supported warning when writing tests with React Testing Library and React hooks.

Background

In React 18, the ReactDOM.render method has been deprecated in favor of createRoot. This fundamental change aims to support concurrent features and future improvements. While this change simplifies certain patterns in React applications, it does require updates in how we write and maintain our tests.

The Warning

When transitioning to React 18, you might encounter the following warning during tests:

[[See Video to Reveal this Text or Code Snippet]]

This warning indicates that the current testing setup is still using the now-deprecated ReactDOM.render method.

Solution

To resolve this, we need to update our testing setup to replace ReactDOM.render with createRoot. Here’s how you can achieve it:

Step-by-Step Guide

Update your index.js or index.tsx:

Replace:

[[See Video to Reveal this Text or Code Snippet]]

With:

[[See Video to Reveal this Text or Code Snippet]]

Modify your testing setup:

Ensure that your testing library setup uses createRoot similarly. If you are using React Testing Library, update your test utilities to accommodate this change.

Example:

[[See Video to Reveal this Text or Code Snippet]]

Using React Testing Library:

React Testing Library already supports React 18, but make sure you are on the latest version. Your tests should look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

React 18 brings in many optimizations and new concurrent features. While the deprecation of ReactDOM.render may seem like a stumbling block initially, transitioning to createRoot is straightforward. Updating your application and testing setup accordingly ensures that you can take full advantage of the latest React features without hitting deprecated code warnings.

By following the steps outlined above, you can resolve the ReactDOM.render is no longer supported warning and maintain compatibility with React 18 in your test suites.