React 18: Hydration failed because the initial UI does not match what was rendered on the server

If you are encountering the error message “Hydration failed because the initial UI does not match what was rendered on the server” when using React 18, don’t worry, you’re not alone. This error typically occurs when the initial HTML markup sent from the server does not match the HTML generated by React on the client-side. In this blog post, we will explore a couple of solutions to fix this issue.

Solution 1: Ensure Consistent HTML Markup

The first solution is to ensure that the initial HTML markup sent from the server matches the HTML generated by React on the client-side. This can be achieved by using server-side rendering (SSR) or static site generation (SSG) techniques.

With SSR, the server generates the initial HTML markup with the help of a server-side rendering framework like Next.js or Gatsby. This ensures that the HTML sent from the server matches the HTML rendered by React on the client-side. Here’s an example of how to implement SSR using Next.js:

{`// pages/index.js

import React from 'react';

function HomePage() {
  return (
    

      
Hello, World!
    
  );
}

export async function getServerSideProps() {
  return {
    props: {},
  };
}

export default HomePage;`}

With SSG, the HTML markup is pre-generated at build time. This ensures that the initial HTML sent from the server matches the HTML rendered by React on the client-side. Here’s an example of how to implement SSG using Next.js:

{`// pages/index.js

import React from 'react';

function HomePage() {
  return (
    

      
Hello, World!
    
  );
}

export async function getStaticProps() {
  return {
    props: {},
  };
}

export default HomePage;`}

Solution 2: Use Suspense with Error Boundaries

If you are unable to ensure consistent HTML markup between the server and the client, you can use React’s Suspense and Error Boundaries features to handle the hydration error gracefully. Suspense allows you to define fallback UI while waiting for data to load, and Error Boundaries catch errors and display a fallback UI instead of crashing the whole application.

Here’s an example of how to use Suspense with Error Boundaries:

{`import React, { Suspense } from 'react';

const MyComponent = React.lazy(() => import('./MyComponent'));

function App() {
  return (
    
      
        
      
    
  );
}

export default App;`}

In this example, the Suspense component wraps the component that may cause the hydration error. The fallback prop defines the UI to display while waiting for the component to load. The ErrorBoundary component catches any errors thrown by the wrapped component and displays a fallback UI instead of crashing the application.

By using Suspense with Error Boundaries, you can gracefully handle the hydration error and provide a better user experience.

Hopefully, one of these solutions helped you resolve the “Hydration failed because the initial UI does not match what was rendered on the server” error in React 18. Remember to ensure consistent HTML markup between the server and the client or use Suspense with Error Boundaries to handle the error gracefully.