Help me refactoring this code

Question

function func(s, a, b) {
if (s.match(/^$/)) {
return -1;
}
var i = s.length -1;
var aIndex = -1;
var bIndex = -1;
while ((aIndex == -1) && (bIndex == -1) && (i > 0)) {
if (s.substring(i, i +1) == a) {
aIndex = i;
}
if (s.substring(i, i +1) == b) {
bIndex = i;
}
i = i - 1;
}
if (aIndex != -1) {
if (bIndex == -1) {
return aIndex;
}
else {
return Math.max(aIndex, bIndex);
}
}
if (bIndex != -1) {
return bIndex;
}
else {
return -1;
}
}

Answer 1

to attract more answer you'll meed to
1 save it in code bits/playground
2 use indentation
and finally, edit the question by linking the code here, and explain what the code does

at the current state is kinda hard to see whats going on, some potential answerer may leave without analyzing your code at all.