Angularjs - How to check undefined from select value -

how check or trap undefined select value select tag. prevent user forget select selection box.

have been trying below js still show undefined error in console log , not alert show in browser.

code

<select ng-model="add.partcode" ng-options="x.part_no x in distictpartcode" ng-change="getlocation()">     <option value="">please select partcode</option> </select> 

js

if(!angular.isundefinedornull($scope.add.partcode.part_no )){     var partcode = $scope.add.partcode.part_no;   }else {     var alertpopup = $ionicpopup.alert({       title: 'error ...',       template: 'please choose part code first.'     });   } 

or

if(!$scope.add.partcode.part_no){     var partcode = $scope.add.partcode.part_no;   }else {     var alertpopup = $ionicpopup.alert({       title: 'error ...',       template: 'please choose part code first.'     });   } 

error in console.

typeerror: cannot read property 'part_no' of undefined

that's becuse $scope.add.partcode become object when object selected otherwise it's null , null don't have property access them using .

try this

if (!$scope.add.partcode) {   var alertpopup = $ionicpopup.alert({     title: 'error ...',     template: 'please choose part code first.'   }); } else {   var partcode = $scope.add.partcode.part_no; }