Navigating the Angular Controller life cycle

Question

Navigating the Angular Controller life cycle

I have set up my application states using ui-router:

$stateProvider
  .state('app', {
    abstract: true,
    views: {
      'nav@': {
        templateUrl: 'app/navbar.html',
        controller: 'NavbarController',
        controllerAs: 'vm'
      },
      'main@': {
        template: '<div ui-view></div>'
      }
    }
  })
  .state('child1', {
    url: '/child1',
    parent: 'app',
    templateUrl: 'app/child1.html',
    controller: function($timeout) {
      $timeout(function() {
        alert('from child_1');
      }, 15000)
    },
    controllerAs: 'vm'
  })
  .state('child2', {
    url: '/child2',
    parent: 'app',
    templateUrl: 'app/child2.html',
    controller: 'ctrl_2',
    controllerAs: 'vm'
  })

After navigating quickly from /child1 to /child2 (before 15000 milliseconds), I still see the alert message defined in the child1 controller. Is this expected behavior?

javascript angularjs angular-ui-router

Answer 1

Answer №1

Is it common for this behavior to occur?

Absolutely, this is completely normal behavior. When function references are created and passed to another function (like the $timeout service), they will remain active as long as that other function holds onto them. In the case of the $timeout service, it will maintain that reference for the specified timeout period (in this scenario, 15 seconds).

Furthermore, if the child function utilizes local variables from the parent function, those variables will persist throughout the lifetime of the child function. This concept is known as "creating a closure".

For more detailed information, you can refer to MDN JavaScript Reference - Closures

It is crucial to inform the $timeout service to cancel the timeout and release the reference; otherwise, it may outlast the controller's lifespan.

controller: function($timeout, $scope) {
  var promise = $timeout(function() {
    alert('from child_1');
  }, 15000);
  $scope.$on("$destroy", function() {
    promise.cancel();
  });
},

In the example above, the $timeout service adds a function named cancel to the promise it generates. By invoking this function in the client code, it signals the $timeout service to terminate the timeout and release the function reference.

When transitioning from the child1 state to another state with ui-router, the scope of the controller is destroyed. Therefore, the controller should monitor the $destroy event and stop the timeout accordingly.

Answer 2

Is it common for this behavior to occur?

Absolutely, this is completely normal behavior. When function references are created and passed to another function (like the $timeout service), they will remain active as long as that other function holds onto them. In the case of the $timeout service, it will maintain that reference for the specified timeout period (in this scenario, 15 seconds).

Furthermore, if the child function utilizes local variables from the parent function, those variables will persist throughout the lifetime of the child function. This concept is known as "creating a closure".

For more detailed information, you can refer to MDN JavaScript Reference - Closures

It is crucial to inform the $timeout service to cancel the timeout and release the reference; otherwise, it may outlast the controller's lifespan.

controller: function($timeout, $scope) {
  var promise = $timeout(function() {
    alert('from child_1');
  }, 15000);
  $scope.$on("$destroy", function() {
    promise.cancel();
  });
},

In the example above, the $timeout service adds a function named cancel to the promise it generates. By invoking this function in the client code, it signals the $timeout service to terminate the timeout and release the function reference.

When transitioning from the child1 state to another state with ui-router, the scope of the controller is destroyed. Therefore, the controller should monitor the $destroy event and stop the timeout accordingly.

Navigating the Angular Controller life cycle

Answer №1

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