function equals(prevVal, newVal) {
        if (self.isMultiple) {
          if (!angular.isArray(prevVal)) {
            // newVal is always an array when self.isMultiple is true
            // thus, if prevVal is not an array they are different
            return false;
          } else if (prevVal.length !== newVal.length) {
            // they are different if they have different length
            return false;
          } else {
            // if they have the same length, then they are different
            // if an item in the newVal array can't be found in the prevVal
            var prevValHashes = prevVal.map(function(prevValItem) {
              return self.hashGetter(prevValItem);
            });
            return newVal.every(function(newValItem) {
              var newValItemHash = self.hashGetter(newValItem);
              return prevValHashes.some(function(prevValHash) {
                return prevValHash === newValItemHash;
              });
            });
          }
        } else {
          return self.hashGetter(prevVal) === self.hashGetter(newVal);
        }
      }
Remove an option from the select
@param {string} hashKey key within the SelectMenuController.options object, which is an
 instance of OptionController.