code: function(arr, callback) {
  
          var result = arr.map(callback);
  
          return result.filter(function(item) {
              return item !== undefined && item !== null;
          });
      }
docs: map
  
  Custom map function
  That filter undefined and null values
  
  @param  {Array}    arr
  @param  {Function} callback
  @return {Array}