Help with regexp replacing every second comma in the string

Question

I have a string of that displays like this....

1235, 3, 1343, 5, 1234, 1

I need to replace every second comma with a semicolon

i.e.

1235, 3;

Answer 1

var s = '1235, 3, 1343, 5, 1234, 1';
var result = s.replace(/(,[^,]*),/g,"$1;");