how to build it ?
First, you need a Java 8 compatible JDK, then you have to edit the line in the script run_build.js that define where the JDK is
var java_home = "PATH_TO_YOUR_JDK";
then you can build it with the following command
jjs run_build.js -- bootstrap skiptest
How to run the test ?
Why do you need to put a home built version of Nashorn in the boot class path when running jsjs ?
jsjs uses the Nashorn parser API defined by the JEP 236 which is integrated in JDK 9 but not available in JDK 8 (yet ?).
/usr/jdk/jdk1.8.0_40/bin/java -Xbootclasspath/p:lib/nashorn.jar -cp .:classes:lib/asm-debug-all-5.0.3.jar jsjs fun.js
then the generated file, fun.class, can be run using the classical java command
/usr/jdk/jdk1.8.0_40/bin/java -cp classes:. fun
Does jsjs implements any ECMAScript standard ?
No, jsjs semantics is a reduced subset of the ECMASCript 5 (strict mode) semantics with the guarantee to be stable.
What do you mean by stable ?