The most commonly used JavaScript effect on the Web is the image rollover. For the one person with access to the Web who’s never seen one before, an image rollover happens when you move your ...

JavaScript-loaded images can be indexed, Google's Martin Splitt confirms. Learn common indexing issues and best practices to ensure your JS images appear in search.

Its seems simple—Websites should serve the right image to the right screen, high-resolution images to high-resolution devices and low res to the rest. But of course it’s not that simple.

As soon as you create the Image object, and set it's source, the browser starts to download. This is done asyncronously. That is, the x.src = "foo.gif" setting, doesn't halt the browser, until the ...