Mongoose Aggregate within time range

mongoose-aggregate.js

wrapper.aggregate = function(startDate, endDate) {
  var model = mongoose.model('Action');
  model.aggregate([
    {'$match': { cd: { '$gt': startDate, '$lt': endDate }, actionType: 'Click' }},
    {'$group': { _id: '$ad', clk: { '$sum': '$value' }}}
  ]).exec(function(err, results) {
    console.log(results);
  });
}