With JavaScript rendering is the process by which a browser or crawler executes JavaScript code to build the final, visible page. Content that is not already in the delivered HTML only appears after this step.Open glossary entry →, content, links or metadata are not delivered directly by the server but generated by JavaScript running in the browser. For human users this is usually invisible, since the browser reliably executes the code.
For search engines, rendering is an extra processing step. Google can execute JavaScript, but it must both Crawling is the process by which a search engine bot fetches a URL and downloads its content. It is the first step before a page can be indexed.Open glossary entry → and render the page. This costs more resources and is more error-prone than reading HTML directly. If rendering fails, for example due to blocked resources, slow application programming interfaces (An application programming interface (API) is an interface through which software systems communicate and exchange data. It defines how requests are made and answered.Open glossary entry →) or JavaScript errors, important content may stay invisible.
It becomes critical with:
- content missing from the initial HyperText Markup Language (HTML) is the markup language for web pages. It defines the structure and content of a page, such as headings, paragraphs, links and images.Open glossary entry →,
- Internal linking refers to links that connect pages within the same website. They control how search engines and users find and thematically classify content.Open glossary entry → created only via JavaScript,
- many AI crawlers are automated bots that fetch web pages for AI providers in order to find content, make it available for search functions, retrieve it for answers, or, depending on the provider, use it for model training.Open glossary entry → that do not render JavaScript, or only partially.
As a rule of thumb, core content and signals should be recognisable without rendering.