Couch view comparison - Erlang vs JS

map_reduce.erl

% Map
fun({Doc}) ->
    case proplists:get_value(<<"type">>, Doc, nil) of
        <<"telemetry">> ->
            {Metadata} = proplists:get_value(<<"metadata">>, Doc, {nil}),
            User =  proplists:get_value(<<"user">>, Metadata, nil),
            Year = proplists:get_value(<<"year">>, Metadata, 0),
            Month = proplists:get_value(<<"month">>, Metadata, 0),
            Day = proplists:get_value(<<"day">>, Metadata, 0),
            GregorianDays = calendar:date_to_gregorian_days(Year, Month + 1, Day + 1),
            Date = list_to_binary(lists:concat([Year, "-", Month, "-", Day])),
            {DocDevice} = proplists:get_value(<<"device">>, Doc, {nil}),
            {DeviceInfo} = proplists:get_value(<<"deviceInfo">>, DocDevice, {nil}),
            {App} = proplists:get_value(<<"app">>, DeviceInfo, {nil}),
            {Software} = proplists:get_value(<<"software">>, DeviceInfo, {nil}),
            {MetaVersions} = proplists:get_value(<<"versions">>, Metadata, {nil}),
            Result = {[
              {<<"date">>, Date},
              {<<"id">>,  proplists:get_value(<<"_id">>, Doc)},
              {<<"device">>, {[
                  {<<"deviceId">>,  proplists:get_value(<<"deviceId">>, Metadata, nil)},
                  {<<"userAgent">>,  proplists:get_value(<<"userAgent">>, DocDevice, nil)},
                  {<<"versions">>, {[
                      {<<"apk">>,  proplists:get_value(<<"version">>, App, nil)},
                      {<<"android">>,  proplists:get_value(<<"androidVersion">>, Software, nil)},
                      {<<"cht">>,  proplists:get_value(<<"app">>, MetaVersions, nil)},
                      {<<"settings">>,  proplists:get_value(<<"settings">>, MetaVersions, nil)}
                  ]}}
              ]}},
              {<<"gregorianDays">>, GregorianDays}
            ]},
            Emit(User, Result);
        _ -> nil
    end
end.

% Reduce
fun(Keys, Values, ReReduce) ->
    Calc_max = fun(Value, Acc) ->
        case Acc of
            nil -> Value;
            _ ->
              AccTotalDays = proplists:get_value(<<"gregorianDays">>, element(1, Acc)),
              EmTotalDays = proplists:get_value(<<"gregorianDays">>, element(1, Value)),
              if
                  EmTotalDays > AccTotalDays -> Value;
                  true -> Acc
              end
        end
    end,
    lists:foldl(Calc_max, nil, Values)
end.

map_reduce.js

// Map
function(doc) {
  if (doc.type === 'telemetry') {
    emit(doc.metadata.user, {
      date: `${doc.metadata.year}-${doc.metadata.month}-${doc.metadata.day}`,
      id: doc._id,
      device: {
        deviceId: doc.metadata.deviceId,
        userAgent: doc.device.userAgent,
        versions: {
          apk: doc.device.deviceInfo.app ? doc.device.deviceInfo.app.version : undefined,
          android: doc.device.deviceInfo.software ? doc.device.deviceInfo.software.androidVersion : undefined,
          cht: doc.metadata.versions.app,
          settings: doc.metadata.versions.settings,
        },
      },
    });
  }
}

// Reduce
function (keys, values) {
  let latest = { date: '0000-00-00' };
  values.forEach(function (value) {
    if (value.date > latest.date) {
      latest = value;
    }
  });
  return latest;
}