These notes are for Java developers who want to convert their Java applets or Java applications to JavaScript, allowing continued one-source development of both Java and JavaScript. SwingJS is not a one-time "port" to JavaScript.

It is a system that allows real-time Java-to-JavaScript conversion within Eclipse, with immediate JavaScript testing and debugging in a browser based on code development in Java. Using the java2script/SwingJS Eclipse plug-in, both Java .class files and their equivalent .js files are created simultaneously.

Developers of java2script/SwingJS itself should read README-developers.md

java2script/SwingJS includes an Eclipse plug-in (technically a "drop-in"), net.sf.j2s.core.zip, along with a JavaScript version of the Java Virtual Machine (SwingJS) to allow the rapid and automated production of browser-ready JavaScript versions of Java applications and applets.

See https://github.com/BobHanson/java2script/tree/master/dist and the README file in that directory.