<img> is not replaced with nextjs custom element defined in useMDXComponents

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30-09-2024

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When working with MDX in a Next.js application, one common challenge developers face is ensuring that native HTML elements, like <img>, are replaced correctly by custom components defined in the useMDXComponents hook. This article aims to clarify this problem, showcase a code snippet that reproduces the issue, and provide insights into how to effectively resolve it.

Original Problem Scenario

Here’s an example of the original code snippet that illustrates the problem:

import { MDXProvider } from '@mdx-js/react';
import { useMDXComponents } from 'mdx-next';

const MyCustomImage = (props) => <img {...props} className="my-custom-image" />;

const components = {
  img: MyCustomImage,
};

function MyApp({ Component, pageProps }) {
  return (
    <MDXProvider components={components}>
      <Component {...pageProps} />
    </MDXProvider>
  );
}

export default MyApp;

In this example, you might expect that whenever an <img> tag is used within your MDX content, it would be replaced with the MyCustomImage component. However, if this isn't happening, it signifies that the replacement mechanism is not functioning as intended.

Analyzing the Issue

The potential reasons why <img> is not being replaced with the MyCustomImage component could be multiple:

1. Incorrect MDX Provider Usage: If your component is not wrapped properly with the MDXProvider, it won't recognize the custom components you defined.

2. MDX Content Structure: Ensure that the content you’re rendering includes the <img> tag as expected and is parsed correctly by MDX.

3. Component Export Issues: If the component MyCustomImage isn’t exported correctly or not in the right scope, it won’t be accessible when the MDX is parsed.

Suggested Solutions

To resolve the issue of the <img> tag not being replaced by MyCustomImage, consider the following strategies:

1. Ensure Proper MDXProvider Use: Double-check that all your MDX content is indeed wrapped in the MDXProvider. This is critical for enabling custom component mappings.

   <MDXProvider components={components}>
      {/* Other components or content */}
   </MDXProvider>
   

2. Check the MDX Content: Verify your MDX files to ensure that they are using the correct syntax and that the <img> tags are present where you expect them.

3. Debugging: Use console logging or React Developer Tools to debug whether the components are being rendered as expected and if your MyCustomImage is receiving the appropriate props.

Practical Example

Here's a quick practical example demonstrating how to replace <img> with a custom component:

// components/CustomImage.js
const CustomImage = ({ src, alt }) => (
  <img src={src} alt={alt} className="custom-image-class" />
);

// pages/_app.js
import { MDXProvider } from '@mdx-js/react';
import CustomImage from '../components/CustomImage';

const components = {
  img: CustomImage,
};

function MyApp({ Component, pageProps }) {
  return (
    <MDXProvider components={components}>
      <Component {...pageProps} />
    </MDXProvider>
  );
}

export default MyApp;

This ensures that all <img> tags in your MDX are rendered as CustomImage, allowing you to apply specific styles or behaviors.

Conclusion

In conclusion, replacing <img> tags with custom components in a Next.js application using MDX can be straightforward once you identify the root cause of the problem. By wrapping your content in MDXProvider, checking the structure of your MDX files, and ensuring correct component exports, you can successfully implement this feature.

Useful Resources

• Next.js Documentation
• MDX Documentation
• React Documentation

By following the strategies and examples provided in this article, you should be able to troubleshoot and fix the problem efficiently. Happy coding!