Tutorials on Spas

Many of today's most popular web applications, such as G-Mail and Netflix, are single-page applications (SPAs). Single-page applications deliver highly engaging and exceptional user experiences by dynamically rendering content without fully reloading whole pages. However, because single-page applications generate content via client-side rendering, the content might not be completely rendered by the time a search engine (or bot) finishes crawling and indexing the page. When it reaches your application, a search engine will read the empty HTML shell (e.g., the HTML contains a <div id="root" /> in React) that most single-page applications start off with. For a smaller, client-side rendered application with fewer and smaller assets and data requirements, the application might have all the content rendered just in time for a search engine to crawl and index it. On the other hand, for a larger, client-side rendered application with many and larger assets and data requirements, the application needs a lot more time to download (and parse) all of these assets and fetch data from multiple API endpoints before rendering the content to the HTML shell. By then, the search engine might have already processed the page, regardless of the content's rendering status, and moved on to the next page. For sites that depend on being ranked at the top of a search engine's search results, such as news/media/blogging sites, the performance penalties and slower first contentful paint of client-side rendering may lower a site's ranking. This results in less traffic and business.