Non-critical third-party scripts defer-loaded or async

Synchronous third-party scripts in <head> block HTML parsing from the moment the browser encounters them (ISO-25010 time-behaviour). A page with four analytics and marketing scripts loading synchronously — Google Analytics, Segment, Drift, Intercom — commonly adds 200–400ms of render-blocking time before any content displays. That delay is entirely external to your codebase: network latency, third-party CDN performance, and script execution time are all out of your control, yet they block your page from rendering.

Move all non-critical third-party scripts to async or defer loading. Analytics, chat widgets, and pixel trackers are never critical for initial render:

<!-- async: executes as soon as downloaded, does not block HTML parsing -->
<script async src="https://www.googletagmanager.com/gtag/js?id=GA_ID"></script>

<!-- defer: executes after HTML is parsed, in source order -->
<script defer src="https://cdn.segment.com/analytics.js"></script>

For the heaviest scripts (chat widgets, heatmap tools), delay loading until after the page is interactive:

// src/components/providers.tsx
if (typeof window !== 'undefined') {
  window.addEventListener('load', () => {
    const script = document.createElement('script')
    script.src = 'https://js.intercomcdn.com/shim.latest.js'
    document.body.appendChild(script)
  })
}

With Next.js <Script> component, set strategy="afterInteractive" or strategy="lazyOnload" instead of strategy="beforeInteractive".