How can I list all the fields that are returned in restlet when executing a saved search. For example

var mySearch = search.load({
            id: 'customsearch_my_so_search'
        });
var searchResult = mySearch.run().getRange({
            start: 0,
            end: 100
        });

I know I can get the length to find out how many rows are returned, but how can I see what the field names are that are returned dynamicly?