Next.js

Add the tag to a Next.js app, with Script in its root layout.

With the App Router, add the tag with Next.js’s Script in the root layout, app/layout.js or app/layout.tsx:

import Script from 'next/script';

export default function RootLayout({ children }) {
  return (
    <html lang="en">
      <body>{children}</body>
      <Script data-domain="example.com" src="https://fiveb.ar/js/tally.js" />
    </html>
  );
}

With the Pages Router, put the same Script in pages/_app.js. Script passes data-domain through to the tag it adds, and loads the script once however many pages the visitor moves through. Keep its default strategy, afterInteractive: lazyOnload waits until the browser is idle, and misses visitors who leave before then. See Next.js’s guide to scripts.

Each page the app moves to is counted as a single-page app’s, with nothing more to add.

Once it’s live, check it works.