How to use the node-opcua-constants.VariableIds function in node-opcua-constants

it("should bind an xml-preloaded Extension Object Variable : ServerStatus ", function (done) {
        // in this test, we verify that we can easily bind the Server_ServerStatus object
        // the process shall automatically bind variables and substructures recursively
        var VariableIds = require("node-opcua-constants").VariableIds;
        var makeNodeId = require("node-opcua-nodeid").makeNodeId;

        var serverStatus = addressSpace.findNode(makeNodeId(VariableIds.Server_ServerStatus));
        serverStatus.browseName.toString().should.eql("ServerStatus");

        // before bindExtensionObject is called, startTime property exists but is not bound
        serverStatus.should.have.property("startTime");
        serverStatus.startTime.readValue().value.dataType.should.eql(DataType.Null);
        serverStatus.readValue().value.dataType.should.eql(DataType.Null);

        //Xx value.startTime.should.eql(DataType.Null);
        //xx debugLog("serverStatus.startTime =",serverStatus.startTime.readValue().value.toString());


        serverStatus.bindExtensionObject();

module.exports.NumericRange = require("node-opcua-numeric-range").NumericRange;

module.exports.AccessLevelFlag = require("node-opcua-data-model").AccessLevelFlag;
module.exports.makeAccessLevel = require("node-opcua-data-model").makeAccessLevel;
module.exports.LocalizedText = require("node-opcua-data-model").LocalizedText;
module.exports.coerceLocalizedText = require("node-opcua-data-model").coerceLocalizedText;
module.exports.QualifiedName = require("node-opcua-data-model").QualifiedName;
module.exports.coerceQualifyName = require("node-opcua-data-model").coerceQualifyName;
module.exports.NodeClass = require("node-opcua-data-model").NodeClass;
module.exports.NodeClassMask = require("node-opcua-data-model").NodeClassMask;
module.exports.AttributeIds = require("node-opcua-data-model").AttributeIds;
module.exports.AttributeNameById = require("node-opcua-data-model").AttributeNameById;
module.exports.BrowseDirection = require("node-opcua-data-model").BrowseDirection;

module.exports.VariableTypeIds = require("node-opcua-constants").VariableTypeIds;
module.exports.VariableIds = require("node-opcua-constants").VariableIds;
module.exports.MethodIds = require("node-opcua-constants").MethodIds;
module.exports.ObjectIds = require("node-opcua-constants").ObjectIds;
module.exports.ObjectTypeIds = require("node-opcua-constants").ObjectTypeIds;
module.exports.ReferenceTypeIds = require("node-opcua-constants").ReferenceTypeIds;
module.exports.DataTypeIds = require("node-opcua-constants").DataTypeIds;

// DA
module.exports.standardUnits = require("node-opcua-data-access").standardUnits;
module.exports.makeEUInformation = require("node-opcua-data-access").makeEUInformation;
module.exports.Range = require("node-opcua-data-access").Range;

//
module.exports.get_fully_qualified_domain_name = require("node-opcua-hostname").get_fully_qualified_domain_name;
module.exports.makeApplicationUrn = require("node-opcua-common").makeApplicationUrn;

// services

const LocalizedText       = require("node-opcua-data-model").LocalizedText;
const NodeClass           = require("node-opcua-data-model").NodeClass;

const BrowseDescription   = require("node-opcua-service-browse").BrowseDescription;

const resolveNodeId       = require("node-opcua-nodeid").resolveNodeId;
const NodeId              = require("node-opcua-nodeid").NodeId;
const sameNodeId          = require("node-opcua-nodeid").sameNodeId;
const makeNodeId          = require("node-opcua-nodeid").makeNodeId;
const StatusCodes         = require("node-opcua-status-code").StatusCodes;

const browse_service     = require("node-opcua-service-browse");

const lowerFirstLetter    = require("node-opcua-utils").lowerFirstLetter;

const VariableIds = require("node-opcua-constants").VariableIds;

const debugLog = require("node-opcua-debug").make_debugLog(__filename);

//
// some server do not expose the ReferenceType Node in their address space
// ReferenceType are defined by the OPCUA standard and can be prepopulated in the crawler.
// Pre-populating the ReferenceType node in the crawler will also reduce the network traffic.
//
const ReferenceTypeIds = require("node-opcua-constants").ReferenceTypeIds;

/*=
 *
 * @param arr
 * @param maxNode
 * @private
 * @return {*}

"use strict";
var build_client_server_session = require("$node-opcua/test-helpers/build_client_server_session").build_client_server_session;
var VariableIds = require("node-opcua-constants").VariableIds;

var subscription_service = require("node-opcua-service-subscription");

describe("testing basic Client Server dealing with subscription at low level", function () {
    var g_session;
    var client_server;

    before(function (done) {

        client_server = build_client_server_session(function (err) {
            if (!err) {
                g_session = client_server.g_session;

            }
            done(err);
        });

*/

const _ = require("underscore");
const crypto = require("crypto");

const NodeId = require("node-opcua-nodeid").NodeId;
const sameNodeId = require("node-opcua-nodeid").sameNodeId;

const NodeIdType = require("node-opcua-nodeid").NodeIdType;
const ServerSidePublishEngine = require("./server_publish_engine").ServerSidePublishEngine;
const StatusCodes = require("node-opcua-status-code").StatusCodes;
const NodeClass = require("node-opcua-data-model").NodeClass;
const QualifiedName = require("node-opcua-data-model").QualifiedName;

const DataValue = require("node-opcua-data-value").DataValue;
const VariableIds = require("node-opcua-constants").VariableIds;

const ec = require("node-opcua-basic-types");
const assert = require("node-opcua-assert").assert;
const util = require("util");
const EventEmitter = require("events").EventEmitter;
const eoan = require("node-opcua-address-space");
const makeNodeId = require("node-opcua-nodeid").makeNodeId;
const ObjectIds = require("node-opcua-constants").ObjectIds;

const WatchDog = require("node-opcua-utils").WatchDog;
const theWatchDog = new WatchDog();

const ContinuationPointManager = require("./continuation_point_manager").ContinuationPointManager;

const utils = require("node-opcua-utils");
const debugLog = require("node-opcua-debug").make_debugLog(__filename);

const StatusCodes = require("node-opcua-status-code").StatusCodes;
const StatusCode = require("node-opcua-status-code").StatusCode;


require("node-opcua-common");

const address_space = require("node-opcua-address-space");
const AddressSpace = address_space.AddressSpace;

const generate_address_space = require("node-opcua-address-space").generate_address_space;

const ServerSession = require("./server_session").ServerSession;

const VariableIds = require("node-opcua-constants").VariableIds;
const MethodIds = require("node-opcua-constants").MethodIds;

const ReferenceType = require("node-opcua-address-space").ReferenceType;


const ServerState = require("node-opcua-common").ServerState;
const ServerStatus = require("node-opcua-common").ServerStatus;
const ServerDiagnosticsSummary = require("node-opcua-common").ServerDiagnosticsSummary;

const endpoints_service = require("node-opcua-service-endpoints");
const ApplicationDescription = endpoints_service.ApplicationDescription;

const nodesets = require("node-opcua-nodesets");
exports.standard_nodeset_file = nodesets.standard_nodeset_file;
exports.di_nodeset_filename = nodesets.di_nodeset_filename;
exports.adi_nodeset_filename = nodesets.adi_nodeset_filename;

const assert = require("node-opcua-assert").assert;
const EventEmitter = require("events").EventEmitter;
const util = require("util");

const coerceNodeId = require("node-opcua-nodeid").coerceNodeId;
const VariableIds = require("node-opcua-constants").VariableIds;

const serverStatus_State_Id = coerceNodeId(VariableIds.Server_ServerStatus_State);
const ServerState = require("node-opcua-common").ServerState;
const StatusCodes = require("node-opcua-status-code").StatusCodes;

const debugLog = require("node-opcua-debug").make_debugLog(__filename);
const doDebug = require("node-opcua-debug").checkDebugFlag(__filename);


function ClientSessionKeepAliveManager(session) {
    const self = this;
    self.session = session;
    self.timerId = 0;
}
util.inherits(ClientSessionKeepAliveManager, EventEmitter);
/**