nextjs-legacy/pages/_document.jsx

// This file provides the overall layout of the site via the `render` method.

import Document, { Html, Head, Main, NextScript } from 'next/document'
import newrelic from 'newrelic'

// In order to inject the browser agent we need to perform an asynchronous
// operation. To do that, we need to extend the `Document` object as
// described in
// https://nextjs.org/docs/pages/building-your-application/routing/custom-document#customizing-renderpage
class RootDocument extends Document {
  static async getInitialProps(context) {
    const initialProps = await Document.getInitialProps(context)

    if (newrelic.agent.collector.isConnected() === false) {
      await new Promise((resolve) => {
        newrelic.agent.on("connected", resolve)
      })
    }

    const browserTimingHeader = newrelic.getBrowserTimingHeader({
      hasToRemoveScriptWrapper: true,
      allowTransactionlessInjection: true,
    })

    return {
      ...initialProps,
      browserTimingHeader,
    }
  }

  render() {
    return (
      <Html>
        <Head>
          <script
            type="text/javascript"
            // The body of the script element comes from the async evaluation
            // of `getInitialProps`. We use the special
            // `dangerouslySetInnerHTML` to provide that element body. Since
            // it requires an object with an `__html` property, we pass in an
            // object literal.
            dangerouslySetInnerHTML={{ __html: this.props.browserTimingHeader }}
          />
          <link rel="stylesheet" href="/style.css" />
        </Head>
        <body>
        <Main />
        <NextScript />
        </body>
      </Html>
    )
  }
}

export default RootDocument