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js.js is a JavaScript interpreter in JavaScript. Instead of trying to create aninterpreter from scratch,SpiderMonkey is compiled intoLLVM and thenemscripten translates the output into JavaScript.

See several running demoshere.

Academic paper to appear atWebApps 2012 locatedhere.

The compiled version of js.js is 3MB and only594KB after gzip compression.Using theSunspider benchmark, the interpreter is about200 times slowerthan Spidermonkey's native interpreter with the JIT compiler turned off. Moreoptimizations and benchmarks are coming soon.

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); //2JSJS.End(jsObjs);

More examples are available in theexamples directory.

The following files are located in thesrc directory.

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-minifiedversion (useful for debugging and modifications):

<script type="text/javascript" src="libjs.O2.js"></script><script type="text/javascript" src="jsjs-wrapper.js"></script>