There are only 3 APIs. Two are documented in the Scripted Datasource when you create one - read the comments. It doesn't look like that pattern was followed for the Scripted Extractor.



The 3rd must have been added later and wasn't added to the script template. It is:  


user_state.setVariable(name, value) where name and value are both strings. Java strings, not Javascript strings - IIRC the Java-to-JS bridge doesn't automatically convert them.



At some point JSON support was also added, so you have JSON.parse(String) and JSON.stringify(object) - which are equivalent to the methods available in the browser.