replace() function parameters

[Lewiz]

Hi everyone,

I've been using this expression and it works great, think it was created by Ukramedia but I'm not sure. It adds points to long numbers between every group of three digits.

I have a vague idea how it works, but I would love a literal 'translation' from someone experienced. This is the expression:

num = value; function addCommas(x) {
return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}
addCommas(num)

I focus particularly on the the part from ".replace" onward. I  know the B has something to do with the (right-side) boundary of what follows behind it, a digit, and then there's a negation ("not followed by digit) and then the global replacement of something (must be the specific position between the three-digit groups) with a comma.

Very fuzzy summarized, as you can see. What exactly does this line of code sound like in sequential commands?

[Dan Ebberts]

The part between the forward slashes is a Regular Expression, which has its own cryptic syntax separate from JavaScript, which you can decode with a good RegExp reference. However, I think I'd advise switching to JavaScript's built-in number formating functionality, like this example:

s = effect("Slider Control")("Slider").value;
s.toLocaleString("en-US")

[Lewiz]

Hi Dan, thanks a lot for your reply. I wish one day I would come even close to your expertise. Trying to learn all the time though. 
I already tried that beautiful line (didn't know of it's existence until a couple of days ago) but then I ran into the limitation of not being able to add a .toFixed(0) as well, to avoid decimals. You can have one of them, either .toLocaleString or .toFixed but not both. As I couldn't figure out another workaround I choose the above mentioned mystery Java line to be able to add .toFixed later. But there must be a better solution, in combination with .toLocaleString, I think?

Oh yes, I will dive into RexExp as soon as I find a good resource. I want to understand the syntax completely. 

[Dan Ebberts · Accepted solution]

There are optional parameters you can supply to specify how many decimal places (fraction digits), so this would be like toFixed(0):

s = effect("Slider Control")("Slider").value;
s.toLocaleString("en-US",{minimumFractionDigits: 0,maximumFractionDigits: 0})

de 

[Lewiz]

Wow, I totally never knew about nor used these parameters. Didn't even know colons were used anywhere in expressions. Thanks a lot! That certainly opens new possibilities! Gonna play with it right away.