JavaScript rendering
The execution of a page's client-side JavaScript by a search engine so that content and links generated at runtime become indexable.
Technical
Progressive enhancement
A build strategy that starts with working HTML and layers on CSS and JavaScript, so core content and navigation function without scripts.
In full
For SEO progressive enhancement is the cheapest insurance available: if the base layer is semantic HTML with real links and real forms, every crawler, assistive technology and AI agent can consume the page regardless of its rendering capability. It also tends to produce better Core Web Vitals because less JavaScript is required for first meaningful use. The opposite pattern — JavaScript required for anything to exist — makes indexation contingent on a rendering step outside your control.
Example
A filter UI submits a normal GET form when JavaScript fails, so filtered URLs still exist and remain crawlable.
Related terms
Server-side rendering
Generating a page's full HTML on the server for each request, so crawlers and users receive complete markup without executing JavaScript.
Hydration
Attaching client-side JavaScript behaviour to server-rendered HTML so a static page becomes interactive.
Single-page application
An architecture where one HTML shell loads and JavaScript handles all subsequent routing and content updates without full page loads.
Core Web Vitals
Google's set of three field-measured user experience metrics — LCP, INP and CLS — used as part of the page experience signals in ranking.