Say there is an AngularJS controller like this:
var module = angular.module('myApp', []);
module.controller('TimeCtrl', function($scope, $interval) {
var tick = function() {
$scope.clock = Date.now();
window.scope = $scope;
}
tick();
$interval(tick, 1000);
});
Changing $scope.clock would automatically reflect in the DOM.
However, when I do it in the console, I need to do explicitly do
$scope.apply. Why is it so? Is $interval doing some magic?
In general, don't I need to $scope.watch these variables? I thought the purpose of $scope.watch was this.
1.
$interval(f, time)
is more or less
setInterval(function() {
f();
$rootScope.$apply();
}, time)
2.
<div>{{test}}</div>
is more or less
$scope.$watch('test', function(value) {
divElement.innerHTML = value;
})
Why is it so? Is $interval doing some magic?
Yes, it is. It is triggering automatically the AngularJS digest cycle, something you do "manually" with the $scope.$apply() (which also triggers it). This causes the changes to be reflected in the DOM. If the digest cycle is not triggered, AngularJS "does not know changes have been made in the model, so it does not update the DOM".
(...) don't I need to watch these variables?
No, unless you need to be notified when any of these variables have changed their values. As long as you do all changes inside the AngularJS scope the DOM will always be "notified" (updated).
How to know when I am doing the thing inside the AngularJS scope?
Usually when you use functions provided by services such as $interval and $timeout, you're doing things inside the scope, because these are wrappers of the original (setInterval and setTimeout) and trigger automatically the mentioned digest cycle, keeping things synced between model and DOM.
So, finally,
Why do we need $scope.apply() when doing a change from console but not
otherwise?
Because from console you are doing some changes outside the AngularJS scope and need to trigger the mentioned digest cycle by yourself.
The problem: Using a this.promise.then(function(){}) function inside a controller method seems to create a $rootScope:infDig loop although the returned value of that method does not change. It's worth noting that the infinite digest loop is gone when removing the .then() line (see code).
The code:
{{ getSelectedProjects() }} in the view and the following method in the attached controller
var vm = this;
vm.getSelectedProjects = function() {
if (angular.isUndefined(vm.hello)) {
vm.hello = "hello"
vm.promise = $q.when("hello i am a resolved promise")
}
vm.promise //In my original code, this promise is returned by a service (MyService.getPromise()). The resolved value of the returned promise may change which is why the service needs to be called at each digest cycle.
.then(function (ans) {
vm.hello = ans;
}); //remove .then(...) function and there is no infinite digest loop anymore
return vm.hello;
}
The question: Why is this creating an infinite digest loop although the returned value does not change ? How can I avoid it (I badly need the result of that promise)?.
My shaky thoughts: I guess it has to do with the fact .then() each time returns a new promise. The documentation does not state it, but if that promise is each time attached to the controller object (vm), this might be considered as a state change of the controller and trigger a new digest loop, which re-evaluates vm.getSelectedProjects() and again attaches a new promise to the controller, etc.
EDIT
My hypothesis in "shaky thoughts" does not seem fully correct or complete, as the problem persists with this code:
vm.getSelectedProjects = function() {
if (angular.isUndefined(vm.hello)) {
vm.hello = "hello"
}
$q.when("hello i am a resolved promise")//this object is not attached to the controller object
.then(function () {});
return vm.hello;
}
Based on the problems encountered and the comments we created coding guidelines for working with promises in our project. Found it interesting to share it as I haven't seen this documented anywhere.
Coding guideline: Working with promises
Use of promises
Promises are amazing objects, however a wrong use can create headaches. Therefore we have a few guidelines :
Do not use promises in views
Do not use promises in controllers, except in functions called by event handlers (click, init, etc.), the controller construction function (=executed only once) or in animations
If a promise result is used in a view, the model (or the manager) should contain a property that is empty by default and set to the resolved value when the promise is resolved. The controller just returns that value.
Implementation
This is the kind of structure that should be in the model, manager, or other service, as close as possible to the data source. NOT in controllers :
var myApiMethod = function() {
//We call "caching" the fact that this method is executed only if $scope.item is undefined.
If (angular.isUndefined($scope.item) {
$scope.item = {}
$http(xxx).then(function(value){
$scope.item = value;
});
return $scope.item
}
}
The controller then just returns the answer of myApiMethod. You might need to check if 'myService.myApiMethod() != {}'.
In the service we can define a caching behaviour (ex: retrieve data from backend every 2 hours, at a certain event clear the cache, etc. ). As long as there is only one single source of truth (coming from the service in this case, not from the controller) concerning the object to be returned you can easilly play around with this.
Argumentation
*Why not to use promises in views or in controller methods called by expression evaluations (e.g., {{ vm.getMyApiMethodResult() }} *:
Including promises in views is a feature that has been desactivated in Angular 1.x
If myApiMethod is put in the controller without the caching and then used in an expression evaluation (e.g., {{ myCtrl.getMyApiMethod() }} ), it will create an infinite digest cycle, because the resolution of the promise will trigger a new digest cycle, that will again call the vm.getMyApiMethod() function, etc. (more info in this SO answer )
Why not put myApiMethod in t he controller with the caching (like implementation above) to make sure myApiMethod is called only once and avoid the infinite digest loop? Three reasons:
if the response of myApiMethod() changes into a new object, $scope.item will not be updated.
Another drawback of this (that we used a lot in the past, you might still see wrong implementations in the code) is that it creates a lot of duplicate code as we need to duplicate this quite heavy code structure (that can become much more complex when several promises are involved) in all controllers calling myApiMethod()
If you "cache" in the controller, you might end up with different controllers returning different answers although they both return the answer from the same service 'myApiMethod' but at different moments in time.
Remember : This guideline only applies to controller functions called in expression evaluations. You might need promises in controller functions called by event handlers (click, etc.) and that's fine because these functions are not called at each of angular's digest cycles.
Is this a bug in Angular or am I missing something:
Calling a function from the directive's template shows that that function is executed 11 times ! with a templateurl, and 22 times !! with a string template.
angular.module('testDirective', [])
.directive('myDirective', function() {
return {
scope:{},
template: '{{increment()}} {{count}}',
controller: function($scope) {
$scope.count = 0;
$scope.increment = function() {
$scope.count += 1;
};
}
};
})
HTML:
<body ng-app="testDirective">
<my-directive></my-directive>
</body>
RESULT:
22
Here is a Plunker with both template and templateUrl methods.
This is quite an issue when method calls are involved within repeaters as an example, this ends up calling the same method dramatically more time than it should.
Anybody could shed some light on this ?
{{increment()}} in your view is going to be called every time the digest cycle is called, like any bound expression would be. If you were incrementing in the controller function itself, rather than a bound function called from the view template, that would indicate that the directive was "loading" multiple times. But the nature of Angular is that any bound expression is going to be checked for changes repeatedly during the digest cycle, and anything you expect to happen only once (or even a predictable number of times) should never happen inside an expression bound to a content element. On the other hand, expressions bound to event handlers only execute when the event fires.
The model takes some time to get used to. Though the old documentation argued against it, you can use functions in content binding expressions, but they should never change state. You have no real control over when $digest() is called, and if you're thinking in the Angular way, you won't want to.
I also found this post which relates to the same issue to be useful :
Using ng-class with a function call - called multiple times
Also one-time binding can be a solution is some case as related here :
Angular lazy one-time binding for expressions
increment() is being called every time the view is being updated. On load, increment() is called, and the count goes up by 1 which causes the view to be updated and increment() to be called again.
If you look in your console, you will see that Angular is telling you that it's stuck in an infinite $digest loop.
I'm finding that I need to update my page to my scope manually more and more since building an application in angular.
The only way I know of to do this is to call $apply() from the scope of my controllers and directives. The problem with this is that it keeps throwing an error to the console that reads :
Error: $digest already in progress
Does anyone know how to avoid this error or achieve the same thing but in a different way?
From a recent discussion with the Angular guys on this very topic: For future-proofing reasons, you should not use $$phase
When pressed for the "right" way to do it, the answer is currently
$timeout(function() {
// anything you want can go here and will safely be run on the next digest.
})
I recently ran into this when writing angular services to wrap the facebook, google, and twitter APIs which, to varying degrees, have callbacks handed in.
Here's an example from within a service. (For the sake of brevity, the rest of the service -- that set up variables, injected $timeout etc. -- has been left off.)
window.gapi.client.load('oauth2', 'v2', function() {
var request = window.gapi.client.oauth2.userinfo.get();
request.execute(function(response) {
// This happens outside of angular land, so wrap it in a timeout
// with an implied apply and blammo, we're in action.
$timeout(function() {
if(typeof(response['error']) !== 'undefined'){
// If the google api sent us an error, reject the promise.
deferred.reject(response);
}else{
// Resolve the promise with the whole response if ok.
deferred.resolve(response);
}
});
});
});
Note that the delay argument for $timeout is optional and will default to 0 if left unset ($timeout calls $browser.defer which defaults to 0 if delay isn't set)
A little non-intuitive, but that's the answer from the guys writing Angular, so it's good enough for me!
Don't use this pattern - This will end up causing more errors than it solves. Even though you think it fixed something, it didn't.
You can check if a $digest is already in progress by checking $scope.$$phase.
if(!$scope.$$phase) {
//$digest or $apply
}
$scope.$$phase will return "$digest" or "$apply" if a $digest or $apply is in progress. I believe the difference between these states is that $digest will process the watches of the current scope and its children, and $apply will process the watchers of all scopes.
To #dnc253's point, if you find yourself calling $digest or $apply frequently, you may be doing it wrong. I generally find I need to digest when I need to update the scope's state as a result of a DOM event firing outside the reach of Angular. For example, when a twitter bootstrap modal becomes hidden. Sometimes the DOM event fires when a $digest is in progress, sometimes not. That's why I use this check.
I would love to know a better way if anyone knows one.
From comments:
by #anddoutoi
angular.js Anti Patterns
Don't do if (!$scope.$$phase) $scope.$apply(), it means your $scope.$apply() isn't high enough in the call stack.
The digest cycle is a synchronous call. It won't yield control to the browser's event loop until it is done. There are a few ways to deal with this. The easiest way to deal with this is to use the built in $timeout, and a second way is if you are using underscore or lodash (and you should be), call the following:
$timeout(function(){
//any code in here will automatically have an apply run afterwards
});
or if you have lodash:
_.defer(function(){$scope.$apply();});
We tried several workarounds, and we hated injecting $rootScope into all of our controllers, directives, and even some factories. So, the $timeout and _.defer have been our favorite so far. These methods successfully tell angular to wait until the next animation loop, which will guarantee that the current scope.$apply is over.
Many of the answers here contain good advices but can also lead to confusion. Simply using $timeout is not the best nor the right solution.
Also, be sure to read that if you are concerned by performances or scalability.
Things you should know
$$phase is private to the framework and there are good reasons for that.
$timeout(callback) will wait until the current digest cycle (if any) is done, then execute the callback, then run at the end a full $apply.
$timeout(callback, delay, false) will do the same (with an optional delay before executing the callback), but will not fire an $apply (third argument) which saves performances if you didn't modify your Angular model ($scope).
$scope.$apply(callback) invokes, among other things, $rootScope.$digest, which means it will redigest the root scope of the application and all of its children, even if you're within an isolated scope.
$scope.$digest() will simply sync its model to the view, but will not digest its parents scope, which can save a lot of performances when working on an isolated part of your HTML with an isolated scope (from a directive mostly). $digest does not take a callback: you execute the code, then digest.
$scope.$evalAsync(callback) has been introduced with angularjs 1.2, and will probably solve most of your troubles. Please refer to the last paragraph to learn more about it.
if you get the $digest already in progress error, then your architecture is wrong: either you don't need to redigest your scope, or you should not be in charge of that (see below).
How to structure your code
When you get that error, you're trying to digest your scope while it's already in progress: since you don't know the state of your scope at that point, you're not in charge of dealing with its digestion.
function editModel() {
$scope.someVar = someVal;
/* Do not apply your scope here since we don't know if that
function is called synchronously from Angular or from an
asynchronous code */
}
// Processed by Angular, for instance called by a ng-click directive
$scope.applyModelSynchronously = function() {
// No need to digest
editModel();
}
// Any kind of asynchronous code, for instance a server request
callServer(function() {
/* That code is not watched nor digested by Angular, thus we
can safely $apply it */
$scope.$apply(editModel);
});
And if you know what you're doing and working on an isolated small directive while part of a big Angular application, you could prefer $digest instead over $apply to save performances.
Update since Angularjs 1.2
A new, powerful method has been added to any $scope: $evalAsync. Basically, it will execute its callback within the current digest cycle if one is occurring, otherwise a new digest cycle will start executing the callback.
That is still not as good as a $scope.$digest if you really know that you only need to synchronize an isolated part of your HTML (since a new $apply will be triggered if none is in progress), but this is the best solution when you are executing a function which you cannot know it if will be executed synchronously or not, for instance after fetching a resource potentially cached: sometimes this will require an async call to a server, otherwise the resource will be locally fetched synchronously.
In these cases and all the others where you had a !$scope.$$phase, be sure to use $scope.$evalAsync( callback )
Handy little helper method to keep this process DRY:
function safeApply(scope, fn) {
(scope.$$phase || scope.$root.$$phase) ? fn() : scope.$apply(fn);
}
I had the same problem with third parties scripts like CodeMirror for example and Krpano,
and even using safeApply methods mentioned here haven't solved the error for me.
But what do has solved it is using $timeout service (don't forget to inject it first).
Thus, something like:
$timeout(function() {
// run my code safely here
})
and if inside your code you are using
this
perhaps because it's inside a factory directive's controller or just need some kind of binding, then you would do something like:
.factory('myClass', [
'$timeout',
function($timeout) {
var myClass = function() {};
myClass.prototype.surprise = function() {
// Do something suprising! :D
};
myClass.prototype.beAmazing = function() {
// Here 'this' referes to the current instance of myClass
$timeout(angular.bind(this, function() {
// Run my code safely here and this is not undefined but
// the same as outside of this anonymous function
this.surprise();
}));
}
return new myClass();
}]
)
See http://docs.angularjs.org/error/$rootScope:inprog
The problem arises when you have a call to $apply that is sometimes run asynchronously outside of Angular code (when $apply should be used) and sometimes synchronously inside Angular code (which causes the $digest already in progress error).
This may happen, for example, when you have a library that asynchronously fetches items from a server and caches them. The first time an item is requested, it will be retrieved asynchronously so as not to block code execution. The second time, however, the item is already in cache so it can be retrieved synchronously.
The way to prevent this error is to ensure that the code that calls $apply is run asynchronously. This can be done by running your code inside a call to $timeout with the delay set to 0 (which is the default). However, calling your code inside $timeout removes the necessity to call $apply, because $timeout will trigger another $digest cycle on its own, which will, in turn, do all the necessary updating, etc.
Solution
In short, instead of doing this:
... your controller code...
$http.get('some/url', function(data){
$scope.$apply(function(){
$scope.mydate = data.mydata;
});
});
... more of your controller code...
do this:
... your controller code...
$http.get('some/url', function(data){
$timeout(function(){
$scope.mydate = data.mydata;
});
});
... more of your controller code...
Only call $apply when you know the code running it will always be run outside of Angular code (e.g. your call to $apply will happen inside a callback that is called by code outside of your Angular code).
Unless someone is aware of some impactful disadvantage to using $timeout over $apply, I don't see why you couldn't always use $timeout (with zero delay) instead of $apply, as it will do approximately the same thing.
When you get this error, it basically means that it's already in the process of updating your view. You really shouldn't need to call $apply() within your controller. If your view isn't updating as you would expect, and then you get this error after calling $apply(), it most likely means you're not updating the the model correctly. If you post some specifics, we could figure out the core problem.
The shortest form of safe $apply is:
$timeout(angular.noop)
You can also use evalAsync. It will run sometime after digest has finished!
scope.evalAsync(function(scope){
//use the scope...
});
First of all, don’t fix it this way
if ( ! $scope.$$phase) {
$scope.$apply();
}
It does not make sense because $phase is just a boolean flag for the $digest cycle, so your $apply() sometimes won’t run. And remember it’s a bad practice.
Instead, use $timeout
$timeout(function(){
// Any code in here will automatically have an $scope.apply() run afterwards
$scope.myvar = newValue;
// And it just works!
});
If you are using underscore or lodash, you can use defer():
_.defer(function(){
$scope.$apply();
});
Sometimes you will still get errors if you use this way (https://stackoverflow.com/a/12859093/801426).
Try this:
if(! $rootScope.$root.$$phase) {
...
You should use $evalAsync or $timeout according to the context.
This is a link with a good explanation:
http://www.bennadel.com/blog/2605-scope-evalasync-vs-timeout-in-angularjs.htm
try using
$scope.applyAsync(function() {
// your code
});
instead of
if(!$scope.$$phase) {
//$digest or $apply
}
$applyAsync Schedule the invocation of $apply to occur at a later time. This can be used to queue up multiple expressions which need to be evaluated in the same digest.
NOTE: Within the $digest, $applyAsync() will only flush if the current scope is the $rootScope. This means that if you call $digest on a child scope, it will not implicitly flush the $applyAsync() queue.
Exmaple:
$scope.$applyAsync(function () {
if (!authService.authenticated) {
return;
}
if (vm.file !== null) {
loadService.setState(SignWizardStates.SIGN);
} else {
loadService.setState(SignWizardStates.UPLOAD_FILE);
}
});
References:
1.Scope.$applyAsync() vs. Scope.$evalAsync() in AngularJS 1.3
AngularJs Docs
I would advise you to use a custom event rather than triggering a digest cycle.
I've come to find that broadcasting custom events and registering listeners for this events is a good solution for triggering an action you wish to occur whether or not you are in a digest cycle.
By creating a custom event you are also being more efficient with your code because you are only triggering listeners subscribed to said event and NOT triggering all watches bound to the scope as you would if you invoked scope.$apply.
$scope.$on('customEventName', function (optionalCustomEventArguments) {
//TODO: Respond to event
});
$scope.$broadcast('customEventName', optionalCustomEventArguments);
yearofmoo did a great job at creating a reusable $safeApply function for us :
https://github.com/yearofmoo/AngularJS-Scope.SafeApply
Usage :
//use by itself
$scope.$safeApply();
//tell it which scope to update
$scope.$safeApply($scope);
$scope.$safeApply($anotherScope);
//pass in an update function that gets called when the digest is going on...
$scope.$safeApply(function() {
});
//pass in both a scope and a function
$scope.$safeApply($anotherScope,function() {
});
//call it on the rootScope
$rootScope.$safeApply();
$rootScope.$safeApply($rootScope);
$rootScope.$safeApply($scope);
$rootScope.$safeApply($scope, fn);
$rootScope.$safeApply(fn);
I have been able to solve this problem by calling $eval instead of $apply in places where I know that the $digest function will be running.
According to the docs, $apply basically does this:
function $apply(expr) {
try {
return $eval(expr);
} catch (e) {
$exceptionHandler(e);
} finally {
$root.$digest();
}
}
In my case, an ng-click changes a variable within a scope, and a $watch on that variable changes other variables which have to be $applied. This last step causes the error "digest already in progress".
By replacing $apply with $eval inside the watch expression the scope variables get updated as expected.
Therefore, it appears that if digest is going to be running anyways because of some other change within Angular, $eval'ing is all you need to do.
use $scope.$$phase || $scope.$apply(); instead
Understanding that the Angular documents call checking the $$phase an anti-pattern, I tried to get $timeout and _.defer to work.
The timeout and deferred methods create a flash of unparsed {{myVar}} content in the dom like a FOUT. For me this was not acceptable. It leaves me without much to be told dogmatically that something is a hack, and not have a suitable alternative.
The only thing that works every time is:
if(scope.$$phase !== '$digest'){ scope.$digest() }.
I don't understand the danger of this method, or why it's described as a hack by people in the comments and the angular team. The command seems precise and easy to read:
"Do the digest unless one is already happening"
In CoffeeScript it's even prettier:
scope.$digest() unless scope.$$phase is '$digest'
What's the issue with this? Is there an alternative that won't create a FOUT? $safeApply looks fine but uses the $$phase inspection method, too.
This is my utils service:
angular.module('myApp', []).service('Utils', function Utils($timeout) {
var Super = this;
this.doWhenReady = function(scope, callback, args) {
if(!scope.$$phase) {
if (args instanceof Array)
callback.apply(scope, Array.prototype.slice.call(args))
else
callback();
}
else {
$timeout(function() {
Super.doWhenReady(scope, callback, args);
}, 250);
}
};
});
and this is an example for it's usage:
angular.module('myApp').controller('MyCtrl', function ($scope, Utils) {
$scope.foo = function() {
// some code here . . .
};
Utils.doWhenReady($scope, $scope.foo);
$scope.fooWithParams = function(p1, p2) {
// some code here . . .
};
Utils.doWhenReady($scope, $scope.fooWithParams, ['value1', 'value2']);
};
I have been using this method and it seems to work perfectly fine. This just waits for the time the cycle has finished and then triggers apply(). Simply call the function apply(<your scope>) from anywhere you want.
function apply(scope) {
if (!scope.$$phase && !scope.$root.$$phase) {
scope.$apply();
console.log("Scope Apply Done !!");
}
else {
console.log("Scheduling Apply after 200ms digest cycle already in progress");
setTimeout(function() {
apply(scope)
}, 200);
}
}
When I disabled debugger , the error is not happening anymore. In my case, it was because of debugger stopping the code execution.
similar to answers above but this has worked faithfully for me...
in a service add:
//sometimes you need to refresh scope, use this to prevent conflict
this.applyAsNeeded = function (scope) {
if (!scope.$$phase) {
scope.$apply();
}
};
The issue is basically coming when, we are requesting to angular to run the digest cycle even though its in process which is creating issue to angular to understanding. consequence exception in console.
1. It does not have any sense to call scope.$apply() inside the $timeout function because internally it does the same.
2. The code goes with vanilla JavaScript function because its native not angular angular defined i.e. setTimeout
3. To do that you can make use of
if(!scope.$$phase){
scope.$evalAsync(function(){
});
}
let $timeoutPromise = null;
$timeout.cancel($timeoutPromise);
$timeoutPromise = $timeout(() => {
$scope.$digest();
}, 0, false);
Here is good solution to avoid this error and avoid $apply
you can combine this with debounce(0) if calling based on external event. Above is the 'debounce' we are using, and full example of code
.factory('debounce', [
'$timeout',
function ($timeout) {
return function (func, wait, apply) {
// apply default is true for $timeout
if (apply !== false) {
apply = true;
}
var promise;
return function () {
var cntx = this,
args = arguments;
$timeout.cancel(promise);
promise = $timeout(function () {
return func.apply(cntx, args);
}, wait, apply);
return promise;
};
};
}
])
and the code itself to listen some event and call $digest only on $scope you need
let $timeoutPromise = null;
let $update = debounce(function () {
$timeout.cancel($timeoutPromise);
$timeoutPromise = $timeout(() => {
$scope.$digest();
}, 0, false);
}, 0, false);
let $unwatchModelChanges = $scope.$root.$on('updatePropertiesInspector', function () {
$update();
});
$scope.$on('$destroy', () => {
$timeout.cancel($update);
$timeout.cancel($timeoutPromise);
$unwatchModelChanges();
});
You can use $timeout to prevent the error.
$timeout(function () {
var scope = angular.element($("#myController")).scope();
scope.myMethod();
scope.$scope();
}, 1);
Found this: https://coderwall.com/p/ngisma where Nathan Walker (near bottom of page) suggests a decorator in $rootScope to create func 'safeApply', code:
yourAwesomeModule.config([
'$provide', function($provide) {
return $provide.decorator('$rootScope', [
'$delegate', function($delegate) {
$delegate.safeApply = function(fn) {
var phase = $delegate.$$phase;
if (phase === "$apply" || phase === "$digest") {
if (fn && typeof fn === 'function') {
fn();
}
} else {
$delegate.$apply(fn);
}
};
return $delegate;
}
]);
}
]);
This will be solve your problem:
if(!$scope.$$phase) {
//TODO
}