Earlier quoted context omitted.
Everyone has a javascript-interpreter installed.
If you are talking about the browser, they are all locked down to prevent JavaScript execution from local files. If you are talking about WScript on Windows (I doubt it), it has an even worse reputation than PowerShell.
Are you talking about Same-Origin-Policy? This shouldn't prevent a script being executed local. It only limits what it can do. Because of security, there is heavy sandboxing with javascript.
Anyway, it wouldn't be hard to transform browsers in full fledged local scripting-engines, without dismanteling security.