Performance Of Closure Compiler On Skulpt

05 Nov 2009

As is flying around today (at least in some very specific circles), Google released the unfortunately named Closure Tools.

There’s 3 components:

I can’t say I care much about the template system, as I haven’t had much occasion to use a templating client-side. But, I need to look at it more to understand what its intended uses are.

The standard library looks pretty decent. I think the most interesting part is definitely goog.ui.* which appears to be most of the UI widgets that are used in the building of Gmail, Maps, etc. There’s some demos via their SVN. These aren’t flashy demos, but there’s broad functionality, and (I assume) broadly cross-browser tested support here, which is a huge time saver.

And the compiler. I’ve been using the popular YUI compressor on Skulpt. It’s easy to use, robust, and gives good compression results.

The Skulpt code seemed like a good test for the Closure compiler. Below, “selfcomp.js” is a debug build of Skulpt (written in Python) compiling itself to JavaScript. This results in a pretty big JS file, weighing in at about a meg. Not unreasonable for a full application though, given that the debug build is heavily commented, and we’re talking pre-minification.

Below is the transcript of a quick Closure compiler test.

~/skulpt$ ls -l support/tmp/selfcomp.js 
-rw-r--r-- 1 sgraham sgraham 965008 2009-11-05 00:21 support/tmp/selfcomp.js

~/skulpt$ time java -jar support/yui/yuicompressor-2.4.2.jar support/tmp/selfcomp.js \
    -o yui.js
real	0m6.340s
user	0m8.393s
sys	0m0.172s

~/skulpt$ time java -jar support/closure-compiler/compiler.jar --js support/tmp/selfcomp.js \
    --js_output_file closure.js
real	4m21.287s
user	4m27.177s
sys	0m1.660s

~/skulpt$ time java -jar support/closure-compiler/compiler.jar --js support/tmp/selfcomp.js \
    --compilation_level ADVANCED_OPTIMIZATIONS --js_output_file closure_adv.js
java.lang.RuntimeException: java.lang.RuntimeException: INTERNAL COMPILER ERROR.

~/skulpt$ gzip closure.js 
~/skulpt$ gzip yui.js

~/skulpt$ ls -l *.gz
-rw-r--r-- 1 sgraham sgraham 24459 2009-11-05 19:11 closure.js.gz
-rw-r--r-- 1 sgraham sgraham 40814 2009-11-05 18:31 yui.js.gz

Yeah, almost four and half minutes to compile vs. 6 seconds for the YUI compressor. I mean, that’s fine, it’s not like you’re doing it on every change, but it’s still long enough to be irritating. It’s as bad as linking on the PS3 or 360!

I haven’t tracked down why the ADVANCED_OPTIMIZATIONS version doesn’t work yet. I’m sure that’s a fixable problem and/or something in the Skulpt-generated code that violates the assumptions that closure-compiler uses. Not too worried about that.

Speed improvements however, would definitely be welcomed.

But, even without the “advanced” optimizations, the end result post-gzipping is pretty awesome. In this case it’s only 60% of the size of the YUI version which is damn impressive.


I was missing some extern declarations that caused the ICE. With those, the advanced version completes successfully, and I’m getting damn near close to a 50% reduction compared to YUI.

-rw-r--r-- 1 sgraham sgraham    21091 2009-11-05 20:48 closure_adv.js.gz