Is this an efficient implementation of the Roman Numeral Converter?
See link above in comments for some more elegant solutions. So I am not going to focus on algorithm, which I think can certainly be improved.

Some thoughts on your code itself:


Comments don't seem to make sense or add value.
No need for all the if-else stuff. Would be much clearer with just if conditions and breaks, IMO.
I don't understand why you build digitArray the way you do. How about something like num.toString().split('').map(function(t){return parseInt(t)}) or Array.from(num.toString()).map(Number) (ES6)?
Your spacing around conditional and flow-control structures (or really, lack thereof) makes your code hard to read.
Indentation is inconsistent.
Seems to be odd use of vertical whitespace.