How to add separator to string at every N characters?

I was having a strange requirements last days and one of them is this one:

we have a string and we want to add a separator after 8 digit.

Here is the post which help me to achieve the my solution:
http://stackoverflow.com/questions/9932096/add-separator-to-string-at-every-n-characters

Solution:

here is the solution that worked for me:

string x = "111111110000000011111111000000001111111100000000";
output should be :
"11111111,00000000,11111111,00000000,11111111,00000000,"

C# : Regex.Replace(myString, ".{8}", "$0,");

Javascript:

"111111110000000011111111000000001111111100000000".replace(/(.{8})/g,"$1,")