JavaScript Rendering: How Jumpple Crawler Sees Your SPA

Two versions of every page

When a crawler requests a URL it first receives the raw HTML from the server. A browser then runs JavaScript, which can add text, links, titles, canonical tags or structured data. Search engines and AI crawlers do not all handle that second step the same way, so it matters which version holds your important content.

What can go wrong with JavaScript SEO?

Pages that depend on scripts can hide problems from tools that read only the raw HTML.

• Main content that exists only after scripts run, leaving a near-empty page in the raw HTML.
• Internal links created by JavaScript that a crawler cannot follow, which creates orphan pages.
• Titles, meta descriptions or canonical tags that change after rendering, so the signal is inconsistent.
• Structured data injected late, which some tools never see.

Compare raw HTML with rendered HTML

Jumpple Crawler includes a JavaScript report that compares the original HTML with the rendered HTML. It lists elements that scripts created or modified, such as the title, H1, meta description, canonical, meta robots, word count and links, along with warnings and errors from the browser.

When you start a crawl through the API you can request JavaScript rendering as an option, so the same comparison is available in automated workflows.

How to fix it

The safest approach is to put the content that matters in the HTML the server sends: the main text, the primary navigation links, the title, the canonical tag and the structured data. Frameworks that support server rendering or static generation make this straightforward.

Two SEO Master checks help here. Content Retrievability looks at how much readable text exists in the page, and No Heavy Script Barrier flags pages where little content is available without running scripts.

A simple routine

Crawl your site, open the JavaScript report, sort by differences in word count or links and review the largest gaps first. After a fix, crawl again and confirm that the raw HTML now carries the content.

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