nice

https://regexr.com/ is a great site for trying out and learning regex.

Check it out.

the c = c > 9 is setting c equal to true if there is digit carried. The true value is coerced to 1 in the next iteration (the c += ... part).

** is the exponentiation operator. It is part of the ES7 proposal. Documentation here.

Explanation: of (/,\s([^,]+)$/)

, -> Find a comma...
\s -> with zero spaces...
([^,]+) -> and one or more non-comma characters at the
$ -> ...end of the string

A cool thing about '~~' is that it will parse a null value or empty string as 0. Very useful here, since the strings can be different lengths.

'~' is a bit operation which inverts bits in number. Bitwise operations works with the integer part of number. So if we use '~~' (double inverting) we get our number in integer representation. In this solution its just rounding number for exclusion zeros before number ('00123' -> '123'). 'c>9' returns true when c>9, true+1 = 2. It's for balance when added.

C = C > 9 probably it's something like carry flag. There are column addition like as

4 +
4

8`

you get just 8 and addition is over, but if you add

5 +
5

10

You add 5 + 5 and get 10, but you can write only one digit, the 0. You have to write 1 too.
But cycle is over because A and B arrays already empty. And result will be 0.
In this case you need check if you have reminder from adding.

C = C > 9 just check if number more 9. I.e C = 5 + 5, C = 10, and then C = 10 > 9, C = true.

In this case a script have to run more one cycle.
And C now is Boolean, true or false then C = C + (~~A.pop() + ~~B.pop()); considering as C = 1 + (number + number) or C = 0 + (number + number)
I.e true + 1 == 2 or true + 0 == 1

Oh it's little difficult even for me. But I hope you can understand basic idea.

~~ it's using for convert any value to integer. For example:

~~undefined = 0, ~~1.1 = 1, ~~"test" = 0 and even ~~null = 0 etc.

It's good hack if you don't want write various conditions such as

if (a != null || a != undefined) you just write c = ~~a and if variable is incorrect,
it's just return 0 in any case without any exception.

I've learned it from a combination of things, but I usually use the mozilla developer documents for reference. Hope this helps! https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace.