Return substring instance count - 2

function searchSubstr( fullText, searchText, allowOverlap ){
  if (arguments.length < 3) {
    allowOverlap = true;
  }
  if (searchText === '') return 0;
  var pos = 0,
      count = 0;
      

  while (fullText.indexOf(searchText, pos) > -1) {
    pos = fullText.indexOf(searchText, pos) + (allowOverlap ? 1 : searchText.length);
     count++;
   }
   return count;
}