As I work on my angularjs application, I find myself utilizing directives for reusable UI elements across different pages. However, I encounter a challenge when a directive depends on a value from a promise. In such cases, I have to employ $scope.$watch along with an if condition to handle undefined values, as the directive compiles before the promise resolves. Here is a snippet of the code:
myAppModule.directive('topicDropdown', function () {
return {
templateUrl: 'Scripts/app/shared/dropdown/tmplTopic.html',
restrict: 'AE',
scope: {
subjectId: '=',
setDefault: '=',
topicId: '='
},
controller: [
'$scope', 'service', function ($scope, service) {
$scope.$watch('subjectId', function () {
if ($scope.subjectId != undefined)
$scope.getTopics();
});
$scope.getTopics = function () {
service.get("section/topics/" + $scope.subjectId).then(function (data) {
$scope.listOfTopics = data;
if ($scope.setDefault) {
$scope.subjectId = $scope.listOfTopics[0].UniqueId;
}
});
}
}
]
}
});
This setup ensures that the subjectId retrieved from a promise prevents any errors due to undefined values during the execution of getTopics.
scope: {
subjectId: '=',
setDefault: '=',
topicId: '='
},
Although this implementation works, it does result in invoking the digest cycle upon every change in the subjectId, potentially causing unnecessary iterations through all watched scopes. At present, I am specifically concerned about changes in the subject ID only.
One alternative approach involves using ng-if within the template HTML, like so:
<div ng-if="subjectId != undefined">
<topic-dropdown subject-id="subjectId"></topic-dropdown>
</div>
By implementing this technique, I can eliminate the need for $scope.$watch, but I remain uncertain whether this is the most optimal solution available.
Do you have any suggestions or insights on how to tackle this issue more effectively? Are there any directive properties that might offer a better solution than those I am currently aware of?
Sincerely, Nick