Benefits of WebStorm over Resharper

Having used Resharper for Asp.Net development, I've concluded that Webstorm is probably not an appropriate option (due to heavy use of C#).  However, the same cannot be said about (Javascript) toolbar development.  As someone who is pretty happy using Visual Studio and Resharper for toolbar development, what major benefits would I see if I switched to Webstorm?

I'd rather not dive into a trial without a high level understanding of what features I should be looking for.