StatisticDefinition

// query for the sum of the population in all features
let sumPopulation = {
  onStatisticField: "POP_2015",  // service field for 2015 population
  outStatisticFieldName: "Pop_2015_sum",
  statisticType: "sum"
}
let query = layer.createQuery();
query.outStatistics = [ sumPopulation ];
layer.queryFeatures(query)
  .then(function(response){
     let stats = response.features[0].attributes;
     console.log("output stats:", stats);
  });

// query for the average of the population change for all features
// Notice that you can pass a SQL expression as a field name to calculate statistics
let populationChangeDefinition = {
  onStatisticField: "POP_2015 - POP_2010",  // service field for 2015 population
  outStatisticFieldName: "avg_pop_change_2015_2010",
  statisticType: "avg"
}
let query = layer.createQuery();
query.outStatistics = [ populationChangeDefinition ];
layer.queryFeatures(query)
  .then(function(response){
     let stats = response.features[0].attributes;
     console.log("Average change:", stats.avg_pop_change_2015_2010);
  });

// query for the average of the population change grouped by regions
// query result will also return an extent for each group encompassing
// all features in each group.
let populationChangeDefinition = {
  onStatisticField: "POP_2015 - POP_2010",  // service field for 2015 population
  outStatisticFieldName: "avg_pop_change_2015_2010",
  statisticType: "avg"
};
let aggregatedExtent = {
  statisticType: "envelope-aggregate"
};
let query = layer.createQuery();
query.groupByFieldsForStatistics = ["Region"];
query.outStatistics = [ populationChangeDefinition, aggregatedExtent ];
layer.queryFeatures(query).then(displayResults);

let query = layer.createQuery();
// find the median value in descending order for response_rate field
// for all features stored in the layer and order
query.outStatistics = [{
  statisticType: "percentile-continuous",
  statisticParameters: {
    value: 0.5,
    orderBy: "DESC"
  },
  onStatisticField: "response_rate",
  outStatisticFieldName: "Resp_rate_median"
}];
// query the features for the median value statistics against the values
// stored in the response_rate field
queryFeatures(query);

// Query the percentile for response time in descending order for all features in the layer
// group the percentile by Division and unit fields
let query = layer.createQuery();
query.orderByFields = ["Division, Unit"];
query.groupByFieldsForStatistics = ["Division, Unit"];
query.outStatistics = [{
  statisticType: "percentile-discrete",
  statisticParameters: {
    value: 0.67,
    orderBy: "DESC"
  },
  onStatisticField: "response_time",
  outStatisticFieldName: "response_time_percentile"
}];
queryFeatures(query);

// average of age fields by regions
const ageStatsByRegion = new StatisticDefinition({
  onStatisticField: field,
  outStatisticFieldName: "avgAge",
  statisticType: "avg"
});

// extent encompassing all features by region
const aggregatedExtent = new StatisticDefinition({
  statisticType: "envelope-aggregate",
  outStatisticFieldName: "aggregateExtent",
});

// group the statistics by Region field
// get avg age by Regions and extent of each region
const query = layer.createQuery();
query.groupByFieldsForStatistics = ["Region"];
query.outStatistics = [consumeStatsByRegion, aggregatedExtent];
layer.queryFeatures(query).then((results) => {
  results.features.forEach((feature) => {
    if (feature.attributes.Region === "Midwest") {
       view.goTo(feature.aggregateGeometries.aggregateExtent);
    }
  });
});