javascript - Error caused when set checkboxes as checked using angularjs -

this html:

<span ng-repeat="category in categories">       <label class="checkbox-inline" for="{{category.id}}">         <input type="checkbox" ng-checked="check(category.id)" ng-click="saverolemenu($event,category.id)" name="group" id="{{category.id}}" />         {{category.name}}       </label> </span> 

this controller:

//get menus authorityservice.getmenus().then(function(response) {     $scope.categories = response.data.data; //get menus success })  //get user's menus var roleid = sessionstorage.getitem("roleid"); authorityservice.getmenusbyroleid(roleid).then(function(response) {     $scope.usermenu = response.data.data; //get user's menu success }) $scope.saverolemenu = function($event, id) {     var checkbox = $event.target;     if (checkbox.checked) {         var roleid = $location.search().id;         authorityservice.saverolemenu(roleid, id).then(function(response) {             if (response.data.code == 0) {                 alert("success！");             }         })     } }  $scope.check = function(value) {     //error caused here     (var = 0; < $scope.usermenu.length; i++) {         if(value == $scope.usermenu[i].id){             return true;         }else{             return false;         }     } } 

i want set checkbox checked if value in $scope.usermenu,but in check function,caused error "cannot read property 'length' of undefined",what's reason error?

cannot read property 'length' of undefined 

means $scope.usermenu not defined. define $scope.usermenu before assigning value it.

$scope.usermenu = []; var roleid = sessionstorage.getitem("roleid");