I should keep the record of these utility functions that I implement many many times…

last_index.js

var lastIndexOf = function (hay, needle) {
  var i = hay.split('').reverse().join('').indexOf( needle.split('').reverse().join('') );
  var result = -1;
  if (i > -1) {
    result = hay.length - (i + needle.length);
  }
  return result;
};