AngularJS - activating $watch/$observe event handlers

I am looking for a way to trigger all $watch/$observe listeners, even if the watched/observed value has not changed. This would allow me to implement a "testing only" feature that refreshes the current page/view without requiring user interaction. I have attempted to use $apply/$digest but it did not work:

$timeout(function(){
    $scope.$apply();
});

$timeout(function(){
    $scope.$digest();
});

Is there an alternative method to achieve this?

Warm regards,

Answer №1

By calling $scope.$apply(), you can initiate a digest cycle which internally invokes $digest. The following example demonstrates manual changes:

The variable number will not be bound as the timeout function takes it out of Angular's scope.

setTimeout(function () { 
    $scope.number = Math.random(); 
});

However, you can "force" it to display by applying scope changes manually:

setInterval(function () {
    $scope.$apply(); 
}, 100);

Demos: No change / Change with manual updates

This method will not activate watchers. In the $digest implementation, it verifies if the value has changed since the previous watch evaluation and triggers the callback only if there has been a change.

if ((value = watch.get(current)) !== (last = watch.last) ... [rootScope.js]

Hence, you must somehow modify the value of the last execution, which is achievable through the $$watchers object on the scope:

$scope.digest = function () {
    setTimeout(function () {
        angular.forEach($scope.$$watchers, function (w) {
            w.last.value = Math.random();
        });

        $scope.$apply();
    });
}

DEMO

Answer №2

Have you considered utilizing the $emit method followed by capturing the event using the $on function?

When we invoke an event with $emit(), it travels upwards from the originating scope to its parent scopes, informing all scopes above about the occurrence of that particular event. This mechanism allows us to communicate changes in state within our application effectively.

_.bind($scope.$emit, $scope, 'myCustomEvent');

Subsequently, on the capture phase:

$scope.$on('myCustomEvent', function() {                            
   // perform a specific task
});

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