“If you’ve used Google Search recently, you may have noticed a
new feature that we’re calling Instant Previews. By clicking on the
(sprited) magnifying glass icon next to a search result you see a
preview of that page, often with the relevant content highlighted.
Once activated, you can mouse over the rest of the results and
quickly (instantly!) see previews of those search results, too.“Adding this feature to Google Search involved a lot of
client-side Javascript. Being Google, we had to make sure we could
deliver this feature without slowing down the page. We know our
users want their results fast. So we thought we’d share some
techniques involved in making this new feature fast.”