Once you have a JavaScript interpreter installed on your system, possibly to provide a server-side or CGI handling mechanism, you can easily use it then to do the things you might previously have done in Perl, Tcl, Bourne, Korn or C-Shell.

Not that you would necessarily choose JavaScript over the other alternatives but for some projects it might be better suited due to the kind of data you are manipulating or what you need to do to it.

The main strength of the Unix environment is the way multiple scripting languages can be used at will and a project may be built from code that runs in many different environments and contexts.

Cross-references:

Wrox Instant JavaScript - page 5