So as you guys might aware, I'm not a pro at JS and recently I had come across a question, where they claimed that the below method can be further reduced and can be written in 4-5 lines max! The original function was little bigger, and I have reduced it to this level.

Can you guys help me out with this?

function func(s, a, b) {
    var match_empty=/^$/ ;
    if (s.match(match_empty))    
        return -1;
    else {
       var aIndex = s.indexOf(a), bIndex = s.indexOf(b);

       if (aIndex != -1)
           return (aIndex != -1) ? ((bIndex == -1) ? aIndex : Math.max(aIndex, bIndex)) : ((bIndex != -1) ? bIndex : -1);
    }        
};