Angular的$ rootScope＃$ digest

Question

Reading this excellent book ( Mastering Web Development in AngularJS ), I ran across this code:

var Restaurant = function ($q, $rootScope) {

var currentOrder;

this.takeOrder = function (orderedItems) {
    currentOrder = {
    deferred:$q.defer(),
    items:orderedItems
};
    return currentOrder.deferred.promise;
};
this.deliverOrder = function() {
    currentOrder.deferred.resolve(currentOrder.items);
    $rootScope.$digest();
};
this.problemWithOrder = function(reason) {
    currentOrder.deferred.reject(reason);
    $rootScope.$digest();
};

My understanding is that the $rootScope.$digest(); calls are made in order to alert Angular that the Promise 's state has been updated.

Is my understanding correct? Also, is it necessary to make the above $rootScope.$digest(); calls?

Answer 1

$scope.$digest() is what processes all of the $watch events that are on the current and children scope. It essentially manually tells the scope to check if a scope variable has changed. You don't generally want to use this when you are inside of a controller or a directive, because the $scope.$apply() function calls the $digest anyway and it is called when you mutate a scope variable.

Checkout this link for an example.

Answer 2

You don't need a $rootScope.$digest here .because resolving/rejecting the promise will fire a $rootScope.$digest internelly, as $intervel , $timeout , $http (after request finished) does that for you. And this $digest can throw errors of $digest already in progress.