01
How JavaScript redirects work
A JavaScript redirect sends the browser to another URL after page scripts execute. It can be useful when application logic genuinely depends on client-side state, but it is different from a server response that immediately tells the crawler a resource has moved.
That difference can add rendering dependency and delay before the destination is discovered.
02
Why server-side redirects are usually preferred
HTTP 301 or 308 responses communicate a permanent move directly and do not require JavaScript execution. They are clearer for browsers, crawlers and debugging, and they work even when scripts fail.
Use a server-side redirect whenever the redirect is fundamentally a URL or content-migration decision.
03
When a JavaScript redirect may be reasonable
Client-side redirects can be appropriate inside web applications where routing depends on authenticated state, a completed action or browser-side logic. Even then, important public URLs should have a crawlable fallback and sensible canonical behaviour.
Avoid using delayed JavaScript redirects as a substitute for fixing URL architecture.
04
Test the final crawl experience
Inspect the network response, rendered DOM, final URL, canonical tag and indexability. Crawl the site with JavaScript rendering enabled and verify that redirect chains do not create loops or inconsistent destinations.
For migrations, monitor how the old URLs are processed after launch rather than assuming the browser behaviour tells the whole story.
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