What Is Prerendering in Chrome?

By this time, you might have read about the new feature that Google introuduced today at the Inside Search media event in San Farancisco, new "Instant Pages," which makes some sites appear to load almost instantly when you click on them from the search results page -- and is enabled by "prerendering," a technology that […]

By this time, you might have read about the new feature that Google introuduced today at the Inside Search media event in San Farancisco, new "Instant Pages," which makes some sites appear to load almost instantly when you click on them from the search results page -- and is enabled by "prerendering," a technology that Google built into the upcoming version of Chrome, currently in the Dev channel.

What's prerendering?

"Sometimes a site may be able to predict with reasonable accuracy which link the user is most likely to click on next--for example, the 'next page' link in a multi-page news article. In those cases, it would be faster and better for the user if the browser could get a head start loading the next page so that when the user clicks the page is already well on its way to being loaded. That's the fundamental idea behind prerendering. The browser fetches all of the sub-resources and does all of the work necessary to display the page. In many cases, the site simply seems to load instantly when the user clicks," explained Google.

"Prerendering, is available to any site. Triggering prerendering well, however, is challenging to do correctly and will only be useful to a handful of sites that've a high degree of certainty of where their users will click next. Triggering prerendering for the wrong site could lead to the link the user did click on loading more slowly."

"The vast majority of sites will automatically work correctly when a third party like Google.com asks Chrome to prerender them. If you're interested in testing how your page behaves when being prerendered you can use this sample page. If you want your page to behave differently, you can use Chrome's new experimental page visibility API to detect prerendering," Google added.

The page visibility API - which's in the early stages of standardization in the webperf working group - can help developers understand the visibility status of their page: whether it's in a foreground tab, a background tab, or being prerendered.

Although the page visibility API is useful for detecting prerendering, it also has many other applications--for example, allowing a site to pause expensive physics calculations when the page isn't visible.

To learn more about the page visibility API and prerendering, you check out Using Page Visibility API and Web Developers' Guide to Prerendering in Chrome articles.

[Source: Chromium blog]