You were able to serve up responsive sites before media queries thanks to Javascript, and now you can extend your responsive sites even further using progressive enhancement and some handy Javascript.
The idea behind JS is to improve the users experience on your site, so remember that what ever you do with JS there is a chance that the user won’t get it… whether that is because of their browser, internal security restrictions, device, or they might be accessing your site via a screen reader.
Foresight.js gives webpages the ability to tell if the user's device is capable of viewing high-resolution images (such as the 3rd generation iPad) before the image has been requested from the server. Additionally, it judges if the user's device currently has a fast enough network connection for high-resolution images.
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