So, I bootstrapped my first React application since the launch of React 18 (6 days after the launch).

When I checked my console, I was seeing an error that I did not expect to find (at least according to me):

Why the error occurs?

The error above is shown when you use React.render() instead of React.createRoot in React v18 to render the root of the application - which is always the div with an id of root in the index.js or index.tsx file; depending on whether you bootstrapped your application to use types (Typescript) or not.

How to fix.

Write the following code in your index.tsx or index.js file

1. Import ReactDOM from the react-dom/client sub-module

Import ReactDOM from 'react-dom/client'

1. Change the structure of your index.js or index.tsx file. However, this will depend on whether your using Typescript or not.

• Using Typescript

import React from 'react'
import ReactDOM from 'react-dom/client'
import App from './App'
import reportWebVitals from './reportWebVitals'

const root = ReactDOM.createRoot(document.getElementById('root') as HTMLElement)
root.render(
 <React.StrictMode>
  <App />
 </React.StrictMode>
)

reportWebVitals()

Look closely and you'll see a createRoot somewhere. Had you seen it? 😏 Pay attention next time :)
The React team changes to createRoot so as to support
Concurrent Mode in React apps.

Concurrent Mode is a set of new features that help React apps stay responsive and gracefully adjust to the user’s device capabilities and network speed.

Read more about concurrent mode

• Using plain Javascript

import React from 'react'
import ReactDOM from 'react-dom/client'
import App from './App'
import reportWebVitals from './reportWebVitals'

const root = ReactDOM.createRoot(document.getElementById('root'))
root.render(
 <React.StrictMode>
  <App />
 </React.StrictMode>
)

reportWebVitals()

Additional information.

• Using React Router in React 18 This is how you would set up your index.js or index.tsx file if you're using the new file set up.

import React from 'react'
import ReactDOM from 'react-dom/client'
import './index.css'
import App from './App'
import reportWebVitals from './reportWebVitals'
import { BrowserRouter } from 'react-router-dom'

const root = ReactDOM.createRoot(document.getElementById('root') as HTMLElement)
root.render(
 <React.StrictMode>
  <BrowserRouter>
   <App />
  </BrowserRouter>
 </React.StrictMode>
)

reportWebVitals()

I hope I helped you in a way I could.

Cheers.

PS: This is the first article I've ever written. To growth 🎉