It's Expensive Being Rich

When you open a web page in a browser, the browser loads the page and all other resources to which the page refers. Some of those resources are files containing JavaScript code, and those files keep getting larger. Some of them can be large enough to noticeably delay the complete loading of the web page, which is a real problem for web site operators. Their dilemma is that users demand features, and JavaScript is a way to provide lots of features, but users also demand that pages load quickly, and adding more and more JavaScript increases the time it takes a page to load. Without changing the underlying technology, it's akin to a zero-sum game, or a game of Whack-a-Mole, or whatever notion you prefer for identifying a situation like this. The two requirements — provide a rich end-user experience, provide it quickly — are to some degree at odds with one another.

Recently James Hamilton pointed out a cool research project which transformed JavaScript source files into a form that allows the source code to be loaded only when needed. Another approach to dealing with this problem — an approach that is complementary to the approach mentioned by Hamilton — is to modify the HTML script element to indicate whether the JavaScript source file needs to be loaded immediately or can be loaded "lazily." This approach exists in the script element section of the HTML 5 draft specification.