Rule Details

JavaScript redirects (using window.location, window.location.href, or window.location.replace) are inefficient and add unnecessary latency to the user experience.

Code Examples

Avoid Client-Side Redirects

// ❌ Bad: Redirecting via JavaScript
if (userIsLoggedIn) {
  window.location.href = '/dashboard';
}

Use Server-Side Redirects

// ✅ Good: Server-side redirect (Next.js Example)
export async function getServerSideProps() {
  if (userIsLoggedIn) {
    return {
      redirect: {
        destination: '/dashboard',
        permanent: false,
      },
    };
  }
}

HTML Meta Redirects

<!-- ⚠️ Avoid if possible, but better than JS -->
<meta http-equiv="refresh" content="0; url=https://example.com/">

Why It Matters

Server-side redirects are the baseline because web.dev's performance guidance (opens in new tab) and crawler behavior both reward fewer client-side hops before the final content is visible.

• Browser Processing: For a JS redirect, the browser must request the page, download the HTML, parse it, and then execute the script before initiating the redirect.
• Latency: This adds at least one full round-trip of latency compared to a server-side redirect, which happens immediately.
• SEO/Crawler Impact: While some modern search engines can follow JavaScript redirects, server-side 301 redirects are much more reliable for transferring SEO value (link equity).
• User Perception: Users may see a momentary "flash" of the original page before the redirect occurs, which is jarring.

Best Practices

✅ Server-Level Redirects: Use your web server configuration (e.g., .htaccess for Apache, nginx.conf for Nginx) or edge configuration (Cloudflare, Vercel). ✅ Handle at Edge: For dynamic redirects based on user state, try to handle them using Edge Functions to minimize the round-trip distance. ✅ Use 301/302 Status Codes: Use the correct HTTP status codes to communicate to both browsers and crawlers whether the redirect is permanent or temporary.

Tools & Validation

• Browser DevTools Network tab to check for 3xx responses.
• Use curl -I "$ORIGIN" or the live target URL to see the redirect headers.
• Ahrefs Redirect Checker (opens in new tab)
• HTTP Status Code Checker (opens in new tab)

Standards

• Use web.dev: Learn Performance as the standard for measuring the final production behavior, not just local synthetic output.
• Use Chrome Developers: Lighthouse overview as the standard for measuring the final production behavior, not just local synthetic output.

Verification

Automated Checks

• Measure the affected page or flow in Lighthouse, PageSpeed Insights, or DevTools and confirm the targeted metric improves.
• Inspect the network waterfall or performance timeline to confirm the intended resource or execution change actually took effect.

Manual Checks

• Verify the change on a throttled mobile profile, not just local desktop.
• If this rule maps to a budget or Web Vital, confirm the page now stays within that threshold.