How to split string while ignoring portion in parentheses?

var regex = /,(?![^(]*\)) /;
var str = "bibendum, morbi, non, quam (nec, dui, luctus), rutrum, nulla"; 

var splitString = str.split(regex);

Here you go. An explanation of the regex:

,     //Match a comma
(?!   //Negative look-ahead. We want to match a comma NOT followed by...
[^(]* //Any number of characters NOT '(', zero or more times
\)    //Followed by the ')' character
)     //Close the lookahead.