find right for google app script

findFromRight.js

// inspired by Chris Rae's VBA site: http://chrisrae.com/vba/

function findRight(findIn, findWhat) {
  var findLoc=0;
  for(findLoc=(findIn.length - findWhat.length + 1);findLoc>=1;findLoc--)
  {
    if (findIn.substring(findLoc,(findLoc + findWhat.length)) === findWhat) {return findLoc;}
  }
  return -1;
}