Small JavaScript that is. Or how to go from 350 kB down to just… 25 kB 23 kB.
Smaller JavaScript can help in up to three ways:
- faster download: faster application installation or startup.
- faster parsing for the browser: faster startup.
- smaller identifiers: faster execution for non-JITting JavaScript engines.
And smaller also means you can have far more complex applications for a given size budget.
Using “Nickel Iron” as illustration
[1]Nickel Iron is now available in the Chrome Web Store [2] and in the Android marketplace [3], it’s built with Smart Mobile Studio [4], using the DWScript [5] JS CodeGen.
The Pascal source for Nickel Iron is made of about 10k lines of code (most of it from the VJL), and a “normal” build, results in 350kB of JavaScript, well formatted, readable and debug-able with clear variable & class names. That’s larger than Pascal source size by about 50%.
Starting from that, if you enable obfuscation, optimization for size and smart linking, the 350 kB go down to 100 kB of a JavaScript source (not really readable anymore), and when that source is packaged in an Android app or sent with HTTP compression, you’ll be looking at a 25 kB file.
For comparison, jQuery [6] is 229 kB raw, and 31 kB minified & compressed, and jQuery UI [7] is about twice larger than jQuery. And when you’ve taken all that baggage, you haven’t done anything yet!
Obfuscation
Obfuscation isn’t just to make your code more annoying to reverse engineer: it can also help make your JavaScript smaller.
When obfuscation is active, the CodeGen will replace most identifiers with shorter versions, usually 1 to 3 characters in length.
Since JavaScript is case sensitive, each extra character added to an identifier can take 62 different values (the CodeGen reserves “$” and “_” for special uses). So obfuscated identifiers are typically short, and that allows to save on space.
JavaScript is also quite heavy on hash-table name lookups, and smaller names help making hash computations faster. On a Desktop JavaScript engine, that advantage quickly fades away as the browser hot-spots profiler decides to JIT, but on your typical Smart-phone browser, the difference can be felt.
Optimize for Size
Optimize for size triggers two mechanisms in the CodeGen:
- a JavaScript “minifier” is run on the output, it will strip away comments, useless spaces, tabs and other characters.
- alternative code generation templates are used, which spit out less readable but smaller code. At this point, there is no choice between size and performance, only between more and less human-readable.
The minifier is applied to “asm” sections too, and performs “safe” minifications only.
Smart Linking
Just like in Delphi, smart linking will eliminate functions methods and classes you have in the Pascal source, but never use in your program.
This is where things break away from other JavaScript libraries in terms of size. At best, they offer manual smart-linking like jQuery UI’s “Build Your Download [8]“, or plain old plug-ins. But if you want to use those, it means you’ll be dealing with manually managing hundreds of different builds (given all the possible combinations), and will probably just be bundling useless stuff sooner or later, because life’s too short and/or time is money.
However, just like in Delphi, Smart Linking works best if your code is well decoupled, if you use dependency-injection and other light-coupling design approaches. So avoid coding spaghetti plates 😉
At the time this article was written, the DWScript Smart-Linker limitations are :
virtual or interfaced methods of a class you use aren’t eliminated (same limitation as in Delphi)update 02/08: now supported, was simpler than anticipated.- there is no de-virtualization just yet (same limitation as in Delphi).
- cross-referencing functions aren’t eliminated (procA calls procB, and procB calls procA), though as this may be more of a sign of a code smell, it might just be getting a compiler “hint” rather than smart-linker support.
Finally, Pascal being declarative and statically-typed (as long as you’re not abusing RTTI/asm stuff), the Smart-Linker will be able to go further than other optimizers that start from JavaScript (like Google’s closure [9]), and thus have to accommodate for all potential dynamic tricks.