Understanding the Error: next/script in _document.js
- In Next.js, the `next/script` component is used for managing the loading of third-party scripts efficiently and optimally. It provides features to enable lazy loading, prioritize script execution, and prevent render-blocking, which enhances the performance of web applications.
- The `_document.js` file in Next.js is a special file used for customizing the default Document structure of a Next.js application. It is responsible for controlling the initial HTML document markup, including ``, ``, and `` tags. It is only rendered on the server side.
- The error "next/script is not allowed in the \_document file" arises due to the logic of separating server-rendered and client-rendered components in Next.js. The `next/script` component is designed to operate with client-side execution, and placing it in `_document.js` conflicts with the server-rendered nature of this file.
- In essence, the `next/script` component needs to access the browser's `window` object for operations like lazy loading and executing scripts when they're needed. Since the `_document.js` file is executed in a server-side context, it does not have access to the `window` object, which is only available on the client side. This is one main reason why it is disallowed in this file.
- Let's look at a minimal example of `_document.js`, where the use of `next/script` would cause an error:
import { Html, Head, Main, NextScript } from 'next/document';
import Script from 'next/script';
class MyDocument extends Document {
render() {
return (
<Html>
<Head>
<Script src="https://example.com/some-external-script.js" strategy="lazyOnload" />
</Head>
<body>
<Main />
<NextScript />
</body>
</Html>
);
}
}
export default MyDocument;
- In the example above, placing `
