Is there a manual for JavaScriptCore shell (jsc)?
There isn't much to the documentation.  It's merely a framework allowing you to run JavaScript from Swift, Objective-C and C based apps.

From Apple Developer:


  The JavaScriptCore Framework provides the ability to evaluate
  JavaScript programs from within Swift, Objective-C, and C-based apps.
  You can use also use JavaScriptCore to insert custom objects to the
  JavaScript environment.


The functions that are supported are referenced here