It's powerful! Without inheritance related JSDoc tags it infers inheritance structures. It tracks multiple definition locations for slots. It provides advanced type inference for 'this' as well as standard JSDT inference.
To learn how to configure see this page: https://bitbucket.org/nexj/webtools.jsdt.core
You can install using this Eclipse update site: https://bitbucket.org/nexj/updatesite/raw/default
Here are some screen shots: http://imgur.com/a/bT4Cd
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