You are calling reactdomclient.createroot() on a container that has already been passed to createroot() before. instead, call root.render() on the existing root instead if you want to update it.

When you see the error message “You are calling ReactDOM.createRoot() on a container that has already been passed to createRoot() before. Instead, call root.render() on the existing root if you want to update it.”, it means that you are trying to create a new root on a container element that has already been used to create a root element.

The function ReactDOM.createRoot() is used to create a new root element for rendering a React application. However, it can only be called once on a specific container element. Once a root element has been created, you should use the render() method of the root element to update the existing root instead of creating a new one.

Here’s an example to explain it further:

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In the above example, we first create a container element with the id “root” using the getElementById() method. Then, we call ReactDOM.createRoot() to create a new root element on the container element. Finally, we use the render() method of the root element to render our React component into the container.

Here’s an incorrect usage that would result in the mentioned error:

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In the incorrect usage example above, we again have the same container element with the id “root”. After creating the first root element on the container, we then try to create another root element using the same container element. This would result in the mentioned error.

To fix the error, you should use the existing root element and call its render() method to update the container:

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In the correct usage example above, we call the render() method on the existing root object (created with createRoot()) to update the container element with our new React component, .