I installed SpiderMonkey on Mac using Homebrew.

$ brew install spidermonkey

Now you can execute JavaScript (from the SpiderMonkey engine) from the console using the js command.

$ js
js> print('お腹すいた' + '、と思ったか？');
お腹すいた、と思ったか？
js> 
js> quit();
$ 

If you want to learn more about SpiderMonkey, please read this:

・SpiderMonkey (JavaScript-C) Engine

That’s all from the Gemba regarding SpiderMonkey installation.