How to use the node-opcua-hostname.resolveFullyQualifiedDomainName function in node-opcua-hostname

public start(callback: (err?: Error) => void) {

        debugLog("RegisterServerManager#start");
        if (this.state !== RegisterServerManagerStatus.INACTIVE) {
            return callback(new Error("RegisterServer process already started")); // already started
        }

        this.discoveryServerEndpointUrl  = resolveFullyQualifiedDomainName(this.discoveryServerEndpointUrl);

        // perform initial registration + automatic renewal
        this._establish_initial_connection((err?: Error) => {

            if (err) {
                debugLog("RegisterServerManager#start => _establish_initial_connection has failed");
                return callback(err);
            }

            this._setState(RegisterServerManagerStatus.REGISTERING);

            this._registerServer(true, (err1?: Error) => {

                if (this.state !== RegisterServerManagerStatus.REGISTERING) {
                    debugLog("RegisterServerManager#start )=> Registration has been cancelled");
                    return callback(new Error("Registration has been cancelled"));

(endpoint as any).__defineGetter__("endpointUrl", () => {
        return resolveFullyQualifiedDomainName(options.endpointUrl);
    });

(endpoint as any).__defineGetter__("endpointUrl", () => {
        return resolveFullyQualifiedDomainName(options.endpointUrl);
    });