Develop Reference

Angular $scope confusion with $watch

I'm still in the beginning stages of my Angular 1.0 journey. I'm learning to like it, but I'm still scratching my head in a few places.
Lately, I've run into something while using $watch that's left me confounded. Take a look:
$scope.$watch('cookies', function() {
if ($cookies.getAll().redditSession) {
$scope.$emit('cookiesChanged')
// $scope.userWelcome = cookieService.decodeCookie($cookies.get('redditSession'))
}
})
$scope.$on('cookiesChanged', function() {
$scope.userWelcome = cookieService.decodeCookie($cookies.get('redditSession'))
})
This code works. If my cookies change, I emit an event thereby triggering the event listener, which changes the value of $scope.userWelcome to some value stored in the cookie. I see this change if I navigate to another route in my app.
However, I'm wondering why I had to use an event emitter here? Notice the line I commented out. I tried this first, but it doesn't change value of $scope.userWelcome, even if I move to another page in my app. I have to reload the page in order to see that I'm logged in.
What's going on here?

Try watching the cookie directly:
$scope.$watch(
function () {
return $cookies.get('redditSession');
},
function (newValue) {
if (newValue) {
$scope.userWelcome = cookieService.decodeCookie(newValue);
};
}
);

Your mistake is that you try to get the new value with the standard method. The way you can actually get the new value is adding it to the parameters of the function. Here it goes:
$scope.$watch('cookies', function(newValue, oldValue) {
if (newValue.getAll().redditSession) {
$scope.userWelcome = cookieService.decodeCookie(newValue.get('redditSession'))
}
// also try this
console.log(oldvalue === $cookies);
});
Cheers!

on enter controller call function angularJS

The problem is that i need to call a function every single time that a route change to a specific state, lets say i have chatController and i have to fire a() every second but if i exit the controller i have to stop a() and when i'm back to chatController i have to restart a()
My code:
$scope.stop = $interval(yourOperation, 1000);
var dereg = $rootScope.$on('$locationChangeSuccess', function() {
$interval.cancel($scope.stop);
dereg();
});
function yourOperation() {
console.log('$location', $location.$$url)
console.log('test');
}
Works fine executing every single and stops when the controller change, but it doesn't work anymore if i go back, i tried with ng-init() function but only fires the first time that the controller start, i need it always when i'm on a specifict controller.

1] If it is state then you can use following event to call function every time when you back to state
$scope.$on('$ionicView.enter',function(){
$scope.callingFunctionName();
});
Here you may need to add following attribute in app.js state declaration
cache: false
2] In case you are using modal then controller will automatically get initialize.
just need to call function like following -
$scope.callingFunctionName();

hi this code must be in the controller
// .... controller
$scope.stop = $interval(yourOperation, 1000);
function yourOperation() {
console.log('hi')
}
$scope.$on('$destroy',function () {
$interval.cancel($scope.stop);
})

angular weirdness with element.click and $location.search

Here is the problem
<div id="my-id" ng-click="moveOn(10)">Click me</div>
In the directive I have
scope.moveOn = function (val) {
$location.search('id', val);
}
And finally in the parent of this directive I listen for a change of this id
$scope.$watch(function () {
return $routeParams.id;
}, function (newId, oldId) {
...
});
This setup works great, after the $location.search is called the $watcher is triggered immediately. But now I also have a directive which does it slightly different, as follows:
element.find('#my-id').click(function (val) {
$location.search('id', val);
});
In the template there is no ng-click!
In this situation I can also see that the call to $location.search is made, but now it takes a very long time (a couple of seconds) before the watcher goes off.
So for some reason there must be a difference between ngClick and binding to a click event. Any suggestions what might be going on here ?

You are updating angular within an event that is outside of angular.
Try using $apply to notify angular of the change so it can run a digest
element.find('#my-id').click(function (val) {
scope.$apply(function(){
$location.search('id', val);
});
});

AngularJS - triggering $watch/$observe listeners

I would like to fire all $watch/$observe listeners even if watched/observed value didn't change. This way I could provide a "testing only" feature to refresh current page/view without user interaction. I've tried to call $apply/$digest but that didn't worked:
$timeout(function(){
$scope.$apply();
});
$timeout(function(){
$scope.$digest();
});
Is there any other way to do it?
Best Regards,

Executing $scope.$apply() will trigger digest cycle as it internally calls $digest, below is example of manual change.
number variable won't get bound as timeout brings it out of angulars scope.
setTimeout(function () {
$scope.number = Math.random();
});
however you can "force" it to show up by manually applying scope changes:
setInterval(function () {
$scope.$apply();
}, 100);
Demos:
No change / Change with manual updates
This will not trigger watchers though. From $digest implementation, it checks if value has changed since the last watch evaluation and will run callback only if it did.
if ((value = watch.get(current)) !== (last = watch.last) ... [rootScope.js]
Therefore you will need somehow change value of the last execution and it's possible to do via $$watchers object on the scope:
$scope.digest = function () {
setTimeout(function () {
angular.forEach($scope.$$watchers, function (w) {
w.last.value = Math.random();
});
$scope.$apply();
});
}
DEMO

How about to use the $emit function then capture that event with $on function?
Within an $emit() event function call, the event bubbles up from the child scope to the parent scope. All of the scopes above the scope that fires the event will receive notification about the event.
We use $emit() when we want to communicate changes of state from within our app to the rest of the application.
_.bind($scope.$emit, $scope, 'myCustomEvent');
then on the capture phase:
$scope.$on('myCustomEvent', function() {
// do something
});

AngularJS : service $broadcast and $watch not triggering on receiving controller

AngularJS noob here, on my path to the Angular Enlightenment :)
Here's the situation:
I have implemented a service 'AudioPlayer' inside my module 'app' and registered like so:
app.service('AudioPlayer', function($rootScope) {
// ...
this.next = function () {
// loads the next track in the playlist
this.loadTrack(playlist[++playIndex]);
};
this.loadTrack = function(track) {
// ... loads the track and plays it
// broadcast 'trackLoaded' event when done
$rootScope.$broadcast('trackLoaded', track);
};
}
and here's the 'receiver' controller (mostly for UI / presentation logic)
app.controller('PlayerCtrl', function PlayerCtrl($scope, AudioPlayer) {
// AudioPlayer broadcasts the event when the track is loaded
$scope.$on('trackLoaded', function(event, track) {
// assign the loaded track as the 'current'
$scope.current = track;
});
$scope.next = function() {
AudioPlayer.next();
};
}
in my views I show the current track info like so:
<div ng-controller="PlayerCtrl">
<button ng-click="next()"></button>
// ...
<p id="info">{{current.title}} by {{current.author}}</p>
</div>
the next() method is defined in the PlayerCtrl, and it simply invokes the same method on the AudioPlayer service.
The problem
This works fine when there is a manual interaction (ie when I click on the next() button) - the flow is the following:
PlayerCtrl intercepts the click and fires its own next() method
which in turn fires the AudioPlayer.next() method
which seeks the next track in the playlist and calls the loadTrack() method
loadTrack() $broadcasts the 'trackLoaded' event (sending out the track itself with it)
the PlayerCtrl listens the broadcast event and assigns the track to the current object
the view updates correctly, showing the current.title and current.author info
However, when the next() method is called from within the AudioService in the 'background' (ie, when the track is over), all the steps from 1 to 5 do happen, but the view doesn't get notified of the change in the PlayerCtrl's 'current' object.
I can see clearly the new track object being assigned in the PlayerCtrl, but it's as if the view doesn't get notified of the change. I'm a noob, and I'm not sure if this is of any help, but what I've tried is adding a $watch expression in the PlayerCtrl
$scope.$watch('current', function(newVal, oldVal) {
console.log('Current changed');
})
which gets printed out only during the 'manual' interactions...
Again, like I said, if I add a console.log(current) in the $on listener like so:
$scope.$on('trackLoaded', function(event, track) {
$scope.current = track;
console.log($scope.current);
});
this gets printed correctly at all times.
What am I doing wrong?
(ps I'm using AudioJS for the HTML5 audio player but I don't think this is the one to blame here...)

When you have a click event the $scope is updated, without the event you'll need to use $apply
$scope.$apply(function () {
$scope.current = track;
});

As it's not safe to peek into the the digest internals, the easiest way is to use $timeout:
$timeout(function () {
$scope.current = track;
}, 0);
The callback is executed always in the good environment.
EDIT: In fact, the function that should be wrapped in the apply phase is
this.loadTrack = function(track) {
// ... loads the track and plays it
// broadcast 'trackLoaded' event when done
$timeout(function() { $rootScope.$broadcast('trackLoaded', track); });
};
Otherwise the broadcast will get missed.
~~~~~~
Actually, an alternative might be better (at least from a semantic point of view) and it will work equally inside or outside a digest cycle:
$scope.$evalAsync(function (scope) {
scope.current = track;
});
Advantage with respect to $scope.$apply: you don't have to know whether you are in a digest cycle.
Advantage with respect to $timeout: you are not really wanting a timeout, and you get the simpler syntax without the extra 0 parameter.

// apply changes
$scope.current = track;
try {
if (!$scope.$$phase) {
$scope.$apply($scope.current);
}
} catch (err) {
console.log(err);
}

Tried everything, it worked for me with $rootScope.$applyAsync(function() {});