Return substring instance count - 2

function searchSubstr( fullText, searchText, allowOverlap ){
  if(fullText == '' || searchText == '') return 0;
  var regex = new RegExp(searchText, 'g'), t = 0, match;
  while(match = regex.exec(fullText)) {
    t++;
    if(allowOverlap) regex.lastIndex = match.index+1;
  }
  
  return t;
}