code: function checkFormatter(formatter, formatterName) {
          if ($.isFunction(formatter)) return true;
          if (!formatter) return false;
          throw new Error(formatterName +" must be a function or a falsy value");
      }
docs: Checks if the formatter function should be used.
  
  Throws an error if it is not a function. Returns true if it should be used,
  false if no formatting should be performed.
  
  @param formatter