Some sites can defer most, if not all, of their JavaScript-driven progressive enhancements until well after the page has loaded. Even so-called “lightweight” libraries like JQuery are far too heavy for some environments…not because they (like Dojo) pull in all the code needed to use them, but because they do it all up-front. Often the best time to pay the expense of loading, parsing, and executing JavaScript code is when the user takes an action that needs the enhancement to run. Dojo already gives you the best tools available anywhere to defer loading modules until you actually use them; other than those provided by dojo.js itself…but what about dojo.js? What if even the small size of Dojo is too big for your page? This need to load as fast as possible and defer work is never greater than in mobile applications. The best-performing thing to do is always to hand-write all the code you’ll need and never use more script than that…but there are complications. Not being able to share your code between developers (let alone between pages) can be a huge disadvantage. The code is also likely to be slow, buggy, and unmaintainable. There’s a real reason why toolkits like Dojo are so incredibly popular: they make much of this pain go away at the cost of initial download size. Why would anyone want to invite the pain back?

So we need some middle ground: a common, expected API surface area combined with a trivial initial footprint to ensure that pages load as fast as possible. How small could we make such a thing? Turns out, 6K.

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