How does mongodb mapreduce page?

  mongodb, question
 map:function(){emit({},this.clickNum);  },
 reduce:function(clickNum,numbers){return Array.sum(numbers);  },

After using the above code to query a total of 300 pieces of data, how to page the collection at this time, for example, 20 pieces per page

Out can be output to a set, and then query and paginate the set.