@123xylem if smaller number preceeds a larger one, both digits make up a number and so you need to skip the next itiration, otherwise you would double count the following digit. E.g. 4 = IV. If you didn't skip you'd count 4 + 5 (IV + V).

cause u add pairs of number in sum

it doesn't need to be converted.
because strings also have the attributes length and index.

So that you may iterate through every object in the array, in this case every roman numeral.

I think it'd be worth adding another variable name to make the code a little more clear. It confused me that you were using the c variable for summing and carrying over a digit. For example, you could say var sum = ~~a.pop() + b.pop() + c instead of c += ~~a.pop() + ~~b.pop(). And then say res = sum % 10 + res

Thanks. And what's the point of saying dot not at the end or end? Wouldn't just saying dot not at end be okay?

Is there any reason for converting the string roman into an aarray?

I'm trying to console log the result object and I can't figure it out. How do you do it?

Good thinking to arrange the order of the letters from least to most common.