The failure is silent
Nothing breaks. The site loads, looks correct and works. But if the substance only exists after JavaScript executes, a crawler that does not execute it sees an empty shell — and increasingly, so does an AI retrieval agent.
Google does render JavaScript, with a delay and a budget. Many other crawlers and most retrieval agents do not, or do so inconsistently. Depending on rendering is therefore a bet on the most capable consumer of your content rather than the typical one.
The one-minute check
View source — the raw document, not the browser inspector. The inspector shows the DOM after JavaScript has run, which is precisely the thing you are trying to test around. If your headline, body copy and links are absent from the raw source, machines may not see them.
Do this on your highest-value commercial page rather than the homepage. Homepages are usually the best-served page on any site.
Three strategies
- Server rendering — HTML built on the server, complete on arrival. The safest default for content that must be found.
- Static generation — pages built at deploy time. Fastest and most reliable, suited to content that does not change per request.
- Client rendering — the browser assembles the page. Appropriate for application interfaces behind a login, rarely appropriate for pages you want indexed.
Most business sites should be static or server-rendered for public content, with client rendering reserved for genuinely interactive components. That is an architecture decision made before build, and expensive to reverse afterwards.
Common traps
- Content behind a tab or accordion is usually fine if it exists in the HTML; content injected only when clicked is not.
- Infinite scroll without paginated URLs makes everything past the first batch unreachable.
- Links implemented as click handlers rather than anchor elements are not links to a crawler.
- Blocking your own JavaScript or CSS in robots.txt prevents rendering being evaluated correctly.
Why this matters more now
Generative engines retrieve passages from the open web, largely without executing JavaScript. A rendering problem that cost you some crawl efficiency five years ago can now remove you from a second surface entirely.