<p>I know that this question has already been asked <a href="https://stackoverflow.com/questions/41207/javascript-interactive-shell-with-completion">HERE</a> but sadly none of the answers suggest a javascript standalone shell that has auto completion.  I am reopening this question again, in the hope that some new answers might be found.</p>

http://www.faqts.com/knowledge_base/view.phtml/aid/1438
lists some JavaScript interpreters.  I am not about to download them to confirm they have (tab?) completion.
[I'm not sure what you mean by auto-completion, since that implies more of an IDE-type approach].
Is this for web-based development/debugging?  If so, I can really recommend the squarefree
JS shell
bookmarklet for Firefox, which was listed in the linked post.  True, it is not standalone, but does have tab completion.