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.

Explanation:

When using ReactDOM.render() to render a React element into a container, you should only call it once on each container.

The error message “You are calling ReactDOM.createRoot() on a container that has already been passed to createRoot() before” occurs when you try to call ReactDOM.createRoot() on a container that has already been passed to it previously.

The correct approach is to use the returned ReactDOMRoot instance and call its render() method whenever you want to update the content.

Here is an example:

    
    <div id="root"></div>
    
    <script>
      const root = ReactDOM.createRoot(document.getElementById('root'));
      
      // Initial rendering
      root.render(
        <div>
          <h1>Hello, World!</h1>
        </div>
      );
      
      // Update
      const updateContent = () => {
        root.render(
          <div>
            <h1>New Content</h1>
          </div>
        );
      }
      
      setTimeout(updateContent, 2000); // Updates the content after 2 seconds
    </script>
    
    

In the example above, we first create a ReactDOMRoot instance using ReactDOM.createRoot(). We then use its render() method to render a React element into the container with id “root”.

The updateContent function is called after 2 seconds using setTimeout. It uses the same root instance to render a different React element, updating the content in the container.

Instead of calling ReactDOM.createRoot() again, we simply call root.render() to update the content.