You've probably already seen this common pattern in action: blurry versions of the images of a site appear immediately and, moments later, their full versions replace them. This pattern has become so common that many image CDNs, frameworks, and libraries support it out of the box. But every implementation has to do the same thing: Fetch both the preview and the final images. Display the preview while the final image loads. Swap the preview and final images. Clean up after the transition. Below is an example of the effect, which shows a blurry preview image. Click the button below to...