问jQuery daterangepicker:执行两次警报？

EN

$(document).ready(
 function(){
 $('#datePicking')
   .daterangepicker({
   arrows:true,
   onClose : function(){
       $('#Viewer')
       alert('ok');
    }
   }); 
});

    $scope.$watch(
    'rangeOfDate',
    function (newValue) {
        // Due to a known bug of open source library daterangepicker, the event is hit twice 
        //upon change. Once it is an object, and once it is a string. So, use appropriately.
        var selectedDateRange = new Object();
        if (typeof (newValue) == 'object') {
            selectedDateRange.startDate = new Date(newValue.startDate).toLocaleDateString();
            selectedDateRange.endDate = new Date(newValue.endDate).toLocaleDateString();
            //Do as you wish with this custom object
        }
        else if (typeof (newValue) == 'string') {
            alert("string");
        }               
    },
    false);