js.js is a JavaScript interpreter in JavaScript. Instead of trying to create an
interpreter from scratch, SpiderMonkey_ is compiled into LLVM_ and then
emscripten_ translates the output into JavaScript.
Demos
See several running demos here <http://jterrace.github.com/js.js/>_.
Paper
Academic paper to appear at
WebApps 2012 <http://static.usenix.org/events/webapps12/>_ located
here <http://www.cs.princeton.edu/~jterrace/docs/jsjs.pdf>_.
Status
The compiled version of js.js is 3MB and only 594KB after gzip compression.
Using the Sunspider_ benchmark, the interpreter is about 200 times slower
than Spidermonkey's native interpreter with the JIT compiler turned off. More
optimizations and benchmarks are coming soon.
Example Use
Here is an example of how to use the API::
var jsObjs = JSJS.Init();
var rval = JSJS.EvaluateScript(jsObjs.cx, jsObjs.glob, "1 + 1");
var d = JSJS.ValueToNumber(jsObjs.cx, rval);
window.alert(d); //2
JSJS.End(jsObjs);
More examples are available in the examples directory.
Files
The following files are located in the src directory.
=================== =========
File Description
=================== =========
js.O0.js Command-line JS shell, no optimizations
js.O0.min.js Command-line JS shell, no optimizations, closure compiled
js.O1.js Command-line JS shell, O1 optimizations
js.O1.min.js Command-line JS shell, O1 optimizations, closure compiled
js.O2.js Command-line JS shell, O2 optimizations
js.O2.min.js Command-line JS shell, O2 optimizations, closure compiled
libjs.O0.js JSAPI shared library, no optimizations
libjs.O0.min.js JSAPI shared library, no optimizations, closure compiled with js.js wrapper
libjs.O1.js JSAPI shared library, O1 optimizations
libjs.O1.min.js JSAPI shared library, O1 optimizations, closure compiled with js.js wrapper
libjs.O2.js JSAPI shared library, O2 optimizations
libjs.O2.min.js JSAPI shared library, O2 optimizations, closure compiled with js.js wrapper
jsjs-wrapper.js js.js wrapper API to make using the JSAPI easier
=================== =========
To run the shell, you want to run one of these::
js js.O2.min.js -e "print('hello');"
node js.O2.min.js -e "print('hello');"
To include the API in your website, include the minified libjs like this::
<script type="text/javascript" src="libjs.O2.min.js"></script>
Alternatively, you can use the wrapper script directly with a non-minified
version (useful for debugging and modifications)::
<script type="text/javascript" src="libjs.O2.js"></script>
<script type="text/javascript" src="jsjs-wrapper.js"></script>
.. _SpiderMonkey: https://developer.mozilla.org/en/SpiderMonkey
.. _emscripten: http://emscripten.org/
.. _LLVM: http://llvm.org/
.. _Sunspider: http://www.webkit.org/perf/sunspider/sunspider.html