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';

s=s.replace(/([^,]+,[^,]+),/g,'$1;')

match anything that is not a comma, followed by a comma, followed by anything that is not a comma, and a comma.

replace everthing inside the parens (which doesn't include the last comma) with itself ('$1'), and add a semicolon in place of that comma.