How JavaScript rendering works
When a search engine fetches a page it first receives the raw HTML the server sent. On a traditional site that file already contains the headings, text and links. On a site built with a JavaScript framework it often contains very little — an empty container and a script that will build the content once it runs in a browser. To see that content, the search engine has to do a second job: load the scripts, execute them, and read the page that results. That second job is rendering.
Google does render JavaScript, but not in the same breath as the fetch. Pages go into a queue and are rendered when resources allow, which is why the gap between publishing and appearing can stretch on a script-dependent site. Other crawlers are less capable: several search engines, and many of the bots behind social previews, link tools and AI assistants, read the raw HTML and nothing more. Whatever your scripts build, they simply never see.
Why JavaScript rendering matters
It decides whether your content exists as far as search is concerned. A page whose main text, headings, internal links, canonical tag or structured data only appear after a script has run is at the mercy of a queue and of each crawler’s capability. Anything that fails to render is not indexed, and a page that is not indexed cannot rank however well it is written.
The cost is felt worst by sites that publish often or change often — a shop with rotating stock, a listings site, a news section. Delay between publish and index is lost revenue, and on mobile connections of the kind most Nepali traffic arrives on, a page that needs a large script bundle before showing anything also loses visitors long before a search engine has an opinion about it.
Where JavaScript rendering goes wrong
The classic failure is navigation that only exists in JavaScript. If links are built by a script, or fire an event handler instead of being real anchor elements with an href, crawlers cannot follow them, and whole sections of a site go undiscovered. Infinite scroll with no linked pagination has the same effect.
Close behind are meta tags, canonical tags and structured data injected by script after load, which are unreliable because they may be read before they appear. Content held behind a click, a tab or a consent step is another; if it takes an interaction to reveal, assume it is not seen. And scripts blocked in robots.txt cannot be executed at all, so the page renders blank even though the file itself is allowed.
How to act on it
Test before you argue about it. Fetch the page as the server sends it and read the raw HTML, or use the URL Inspection tool in Search Console to view the rendered HTML Google actually holds. If the headings, body copy and links are missing from the raw response, you have your answer.
The durable fix is to deliver the important content in the initial HTML — server-side rendering, static generation, or pre-rendering for crawlers, depending on the stack. Whichever route, keep the non-negotiables in the source: title, meta description, canonical, structured data, main copy and real anchor links. Everything else can load afterwards. Rebuilding a rendering strategy after launch is expensive, so it belongs in the technical SEO conversation before a framework is chosen, not after traffic disappoints.