How to use the queue.alertThresholdQueueDepthMessages function in queue

var alertMsgAge = formatter.formatTime( thisObj.vhostData["queue.alertThresholdMessageAge"] );

                       thisObj.alertThresholdMessageAge.innerHTML = alertMsgAge.value;
                       thisObj.alertThresholdMessageAgeUnits.innerHTML = alertMsgAge.units;

                       var alertMsgSize = formatter.formatBytes( thisObj.vhostData["queue.alertThresholdMessageSize"] );

                       thisObj.alertThresholdMessageSize.innerHTML = alertMsgSize.value;
                       thisObj.alertThresholdMessageSizeUnits.innerHTML = alertMsgSize.units;

                       var alertQueueDepth = formatter.formatBytes( thisObj.vhostData["queue.alertThresholdQueueDepthBytes"] );

                       thisObj.alertThresholdQueueDepthBytes.innerHTML = alertQueueDepth.value;
                       thisObj.alertThresholdQueueDepthBytesUnits.innerHTML = alertQueueDepth.units;

                       thisObj.alertThresholdQueueDepthMessages.innerHTML = entities.encode(String(thisObj.vhostData["queue.alertThresholdQueueDepthMessages"]));

                       var stats = thisObj.vhostData[ "statistics" ];

                       var sampleTime = new Date();
                       var messageIn = stats["messagesIn"];
                       var bytesIn = stats["bytesIn"];
                       var messageOut = stats["messagesOut"];
                       var bytesOut = stats["bytesOut"];

                       if(thisObj.sampleTime)
                       {
                           var samplePeriod = sampleTime.getTime() - thisObj.sampleTime.getTime();

                           var msgInRate = (1000 * (messageIn - thisObj.messageIn)) / samplePeriod;
                           var msgOutRate = (1000 * (messageOut - thisObj.messageOut)) / samplePeriod;
                           var bytesInRate = (1000 * (bytesIn - thisObj.bytesIn)) / samplePeriod;