Is JavaScript a good fit for embedded systems?

No, no it's not. Great that's that sorted out. Moving on.

There's quite a few reasons I can think of why you would not want to use JavaScript for embedded systems. It compiles at runtime, its not strongly typed leading to security concerns, debugging it is a nightmare plus a lot of other perfectly valid reasons.

And yet there is only one reason to use JavaScript... "I know JavaScript".

Although I would say that every good programmer needs a lower level language (e.g. Ada, C, C++) under their belt, I can see why they may seem frightening to someone who has came from a front end background.

"What no garbage collection!... wait what's garbage collection, never needed to worry about that before"

These boards by Tessel seem like an ideal point to get into this kind of work as a starting point just as Raspberry Pi got everyone interested again.

tl;dr;

JavaScript for embedded systems? No, unless your a hobbyist and only know JavaScript or because you can "Smash things out with Javascript" and have no concerns.

p.s.

Then again I think languages like php are no good for web development yet are used extensively so what do I know, do what you want.