DataSag guides · Updated 27 October 2026

Load analytics without blocking rendering on Next.js Pages Router

Use the platform's non-blocking external script mechanism and install the tracker once. Measure the published page before and after the change; script size alone cannot predict the effect on your website. This guide applies to Next.js Pages Router.

Start with the Next.js Pages Router installation

Import Script from next/script in pages/_app.tsx. Keep Component and pageProps, and add the tracker once alongside the page component. The shared app stays mounted as users navigate between pages.

Do not install the same tracker in both _app and _document. Do not attach another pageview sender to router.events before testing the tracker's built-in History API handling.

Use the public project key from the DataSag project you are inspecting. A test on a preview domain does not confirm that the production domain has the same code or settings.

Load analytics without blocking rendering in Next.js Pages Router

  1. Keep next/script in pages/_app.tsx with the chosen afterInteractive strategy. Compare that shared installation with any synchronous script left in _document before changing the loading strategy.
  2. Measure the published initial page using a cold load and fixed network settings. Check whether tracker availability precedes the user action you want to observe. A later script load can trade away short-visit coverage.
  3. Follow an internal Link after the initial page settles. Confirm that _app retains the installation and that page changes do not insert another script. Repeat timing measurements on direct entry instead of mixing client navigation with a full-load baseline.

The measured Pages Router baseline uses one shared non-blocking loader and documents the coverage effect of its timing.

Complete the collection checks

  1. Record a baseline of the published page using the same browser, device emulation and network settings you will use for comparison. Include a representative content page, not only the homepage.
  2. Use defer for a normal external HTML script, or the framework-specific loading strategy shown in the installation example. Do not add a parser-blocking synchronous script as a shortcut.
  3. Keep one installation in the shared document or layout. Duplicate execution adds work even if the browser reuses the downloaded file.
  4. Inspect the Network waterfall for tracker.js and /api/track. Compare transfer size, timing and request count on a cold load and a cached load.
  5. Check that measurement still starts at the intended point. Loading only after idle or interaction can omit short visits and early clicks; performance and coverage must be evaluated together.
  6. Repeat the measurements and record variability. Report measured results for your page rather than claiming a universal speed improvement or zero performance cost.
// Browser Console, after loading the published page:
performance.getEntriesByType('resource')
  .filter(entry => entry.name.includes('/tracker.js'))
  .map(entry => ({ url: entry.name, durationMs: entry.duration }));
// Cross-origin transfer details may be unavailable.

What a successful check looks like

The script uses a non-blocking loading mechanism, appears once and records the intended visits. Any performance claim comes from repeatable measurements of the actual site.

Record the public path you tested, the browser state, the approximate time and the observed request. Check one direct page load and one later navigation so the result covers more than the homepage.

Common mistake

A faster lab result does not prove every visitor has a faster experience. Avoid mixing a warm-cache result with a cold-load baseline.

Installation snippet for Next.js Pages Router

The shared installation belongs in pages/_app.tsx, alongside the page component. Use this as the installation reference while checking the procedure above.

import Script from "next/script";

// Alongside <Component {...pageProps} /> in pages/_app.tsx:
<Script
  id="datasag"
  src="https://www.datasag.com/tracker.js"
  data-datasag-key="YOUR_PUBLIC_KEY"
  strategy="afterInteractive"
/>

Related Next.js Pages Router guides

Full Next.js Pages Router setup guide · Search and AI visibility

References

Official Next.js Pages Router documentation covers the integration point. For DataSag data handling, read the privacy policy. Use support if a request fails after these checks.