Call AngularJS from legacy code

Question

I'm using AngularJS to build HTML controls that interact with a legacy Flex application. All callbacks from the Flex app must be attached to the DOM window.

For example (in AS3)

ExternalInterface.call("save", data);

Will call

window.save = function(data){
    // want to update a service 
    // or dispatch an event here...
}

From within the JS resize function I'd like to dispatch an event that a controller can hear. It seems that creating a service is the way to go. Can you update a service from outside of AngularJS? Can a controller listen for events from a service? In one experiment (click for fiddle) I did it seems like I can access a service but updating the service's data doesn't get reflected in the view (in the example an <option> should be added to the <select>).

Thanks!

Tunstall

Note that in the jsfiddle above the injector is obtained without targeting an element within the app using var injector = angular.injector(['ng', 'MyApp']);. Doing this will give you a completely new context and a duplicate myService. That means you'll end up with two instances of the service and model and will be adding data to the wrong place. You should instead target an element within the app using angular.element('#ng-app').injector(['ng', 'MyApp']). At this point you can then use $apply to wrap model changes. – Nameplate

Answer 1

Interop from outside of angular to angular is same as debugging angular application or integrating with third party library.

For any DOM element you can do this:

• angular.element(domElement).scope() to get the current scope for the element
• angular.element(domElement).injector() to get the current app injector
• angular.element(domElement).controller() to get a hold of the ng-controller instance.

From the injector you can get a hold of any service in angular application. Similarly from the scope you can invoke any methods which have been published to it.

Keep in mind that any changes to the angular model or any method invocations on the scope need to be wrapped in $apply() like this:

$scope.$apply(function(){
  // perform any model changes or method invocations here on angular app.
});

Machinist

this works, but I wish there was some way to get from a Module directly to it's scope - is that possible? Having to go back an select the [ng-app] root-node seems backwards when I already have a reference to the Module... – Sanderson

I've run into the same thing recently. I can get to the dom element so it's not a bit deal to get to the scope, just would make more sense to go via the globally registered module. – Packaging

I can't get this to work: I'm calling angular.element(document.getElementById(divName)).scope(), but I am not able to invoke any functions from it, it just returns "undefined" in the console. – Catheterize

works great for me, however I use a class selector, should work fine. – Mohr

@Misko Hevery how do I get to domElement's ng-bind property? – Hydrogenous

Even I'm facing the same problem as described above by @Emil, it's returning undefined. Any help ? – Forewarn

Try listening for the document ready() event before trying to grab anything from Angular – Anatomist

element().scope() will not work if debug data is turned off, which is the recommendation for production. Doesn't that make it useless in this scenario? This will only for testing/debugging. – Vessel

You won't want to do this in Angular 1.3. The Angular team didn't intend to have us calling ".scope()" on elements in production code. It was meant to be a debug tool. So, starting in Angular 1.3, you can turn this off. Angular will stop attaching the scope to the element using jQuery's .data function. This will speed your app up. Additionally, handing off your scopes to jquery's caching features will create memory leaks. So, you should definitely turn this off, to speed up your app. Angular's site has a production guide that you should use to learn more. – Mcgee

To encapsulate the $scope.$apply code, you can put in inside a method on scope like $scope.externalAction = function() {...} and in this method, you can use $scope.$apply. This way, external code does not have to care about calling apply manually or checking if it is in phase or not. – Salmonoid

How good to see someone going straight to the point, without the "you should not do it" without an actual answer. The advice is still valid, but let the one that needs the answer judge if something should or not be done. – Ellinger

how about angular 2.0? it seems to me like if there is no "angular" object in the global context.. – Filberto

Answer 2

Misko gave the correct answer (obviously), but some of us newbies may need it simplified further.

When if comes to calling AngularJS code from within legacy apps, think of the AngularJS code as a "micro app" existing within a protected container in your legacy application. You cannot make calls to it directly (for very good reason), but you can make remote calls by way of the $scope object.

To use the $scope object, you need to get the handle of $scope. Fortunately this is very easy to do.

You can use the id of any HTML element within your AngularJS "micro-app" HTML to get the handle of the AngularJS app $scope.

As an example, let's say we want to call a couple of functions within our AngularJS controller such as sayHi() and sayBye(). In the AngularJS HTML (view) we have a div with the id "MySuperAwesomeApp". You can use the following code, combined with jQuery to get the handle of $scope:

var microappscope = angular.element($("#MySuperAwesomeApp")).scope();

Now you can call your AngularJS code functions by way of the scope handle:

// we are in legacy code land here...

microappscope.sayHi();

microappscope.sayBye();

To make things more convenient, you can use a function to grab the scope handle anytime you want to access it:

function microappscope(){

    return angular.element($("#MySuperAwesomeApp")).scope();

}

Your calls would then look like this:

microappscope().sayHi();

microappscope().sayBye();

You can see a working example here:

http://jsfiddle.net/peterdrinnan/2nPnB/16/

I also showed this in a slideshow for the Ottawa AngularJS group (just skip to the last 2 slides)

http://www.slideshare.net/peterdrinnan/angular-for-legacyapps

Inviting

Note that link-only answers are discouraged, SO answers should be the end-point of a search for a solution (vs. yet another stopover of references, which tend to get stale over time). Please consider adding a stand-alone synopsis here, keeping the link as a reference. – Essence

Beautiful explanation! allowed me to circumvent a form validation by doing this: <input type="button" onclick="angular.element(this).scope().edit.delete();" value="delete"> – Breakfast

Answer 3

Greatest explanation of the concept I've found is situated here: https://groups.google.com/forum/#!msg/angular/kqFrwiysgpA/eB9mNbQzcHwJ

To save you the clicking:

// get Angular scope from the known DOM element
e = document.getElementById('myAngularApp');
scope = angular.element(e).scope();
// update the model with a wrap in $apply(fn) which will refresh the view for us
scope.$apply(function() {
    scope.controllerMethod(val);
}); 

Necropolis

The above works when the app and controller co-exist in the same element. For more complex apps that utilize an ng-view directive to a template, you must get the first element within the view, not the DOM element of the entire app. I had to poke around elements with a document.getElementsByClassName('ng-scope'); node list to figure out the correct scope DOM element to grab. – Discredit

I know this is a really old thread, but I think I am running into this issue. Does anyone have any code that shows how to walk the list to figure out the DOM element to grab? – Retrieval

Ignore my question. I was able to get this work by just using document.getElementById('any-Control-That-Has-An-NG-Directive').scope(). – Retrieval

if you utilize ng-view and split your views into their own files. you can put and id in the top HTML element then do document.getElementById() that id. This gives you access to the scope of that controller. methods/properties etc... just putting a fine point on goosemanjack's comment. – Partly

Answer 4

Thanks to the previous post, I can update my model with an asynchronous event.

<div id="control-panel" ng-controller="Filters">
    <ul>
        <li ng-repeat="filter in filters">
        <button type="submit" value="" class="filter_btn">{{filter.name}}</button>
        </li>
    </ul>
</div>

I declare my model

function Filters($scope) {
    $scope.filters = [];
}

And i update my model from outside my scope

ws.onmessage = function (evt) {
    dictt = JSON.parse(evt.data);
    angular.element(document.getElementById('control-panel')).scope().$apply(function(scope){
        scope.filters = dictt.filters;
    });
};

Diatomic

Answer 5

Further to the other answers. If you don't want to access a method in a controller but want to access the service directly you can do something like this:

// Angular code* :
var myService = function(){
    this.my_number = 9;
}
angular.module('myApp').service('myService', myService);


// External Legacy Code:
var external_access_to_my_service = angular.element('body').injector().get('myService');
var my_number = external_access_to_my_service.my_number 

Chitchat

Answer 6

More safe and performant way especially when debug data is off is to use a shared variable to hold a callback function. Your angular controller implements this function to return its internals to the external code.

var sharedVar = {}
myModule.constant('mySharedVar', sharedVar)
mymodule.controller('MyCtrl', [ '$scope','mySharedVar', function( $scope, mySharedVar) {

var scopeToReturn = $scope;

$scope.$on('$destroy', function() {
        scopeToReturn = null;
    });

mySharedVar.accessScope = function() {
    return scopeToReturn;
}
}]);

Generalized as a reusable directive :

I created a 'exposeScope' directive which works in a similar fashion but usage is simpler:

<div ng-controller="myController" expose-scope="aVariableNameForThisScope">
   <span expose-scope='anotherVariableNameForTheSameScope" />
</div>

This stores the current scope ( that is given to the link function of the directive) in a global 'scopes' object which is a holder for all scopes. Value provided to the directive attribute is used as the property name of the scope in this global object.

See the demo here. As I showed in the demo, you can trigger jQuery events when the scope is stored and removed from the global 'scopes' object.

<script type="text/javascript" >
    $('div').on('scopeLinked', function(e, scopeName, scope, allScopes) {
      // access the scope variable or the given name or the global scopes object
    }.on('scopeDestroyed', function(e, scopeName, scope, allScopes) {
      // access the scope variable or the given name or the global scopes object
    }

</script>

Note that, I haven't tested the on('scopeDestroyed') when the actual element is removed from the DOM. If it does not work, triggering the event on the document itself instead of the element may help. ( see the app.js ) script in the demo plunker.

Salmonoid

Answer 7

I know this is an old question but I was looking at options to do this recently, so I thought I put my findings here in case it's useful to anyone.

In most cases, if there's the need for external legacy code to interact with the state of the UI or the inner workings of the application a service could be useful to abstract away those changes. If an external code is interacting directly with your angular controller, component or directive, you're coupling your app heavily with your legacy code which is bad news.

What I ended up using in my case, is a combination of browser accessible globals (i.e. window ) and event handling. My code has a smart form generation engine which requires JSON output from a CMS to initiliase the forms. Here's what I have done :

function FormSchemaService(DOM) {
    var conf = DOM.conf;

    // This event is the point of integration from Legacy Code 
    DOM.addEventListener('register-schema', function (e) {

       registerSchema(DOM.conf); 
    }, false);

    // service logic continues ....

Form Schema Service is created using angular injector as expected:

angular.module('myApp.services').
service('FormSchemaService', ['$window' , FormSchemaService ])

And in my controllers: function () { 'use strict';

angular.module('myApp').controller('MyController', MyController);

MyEncapsulatorController.$inject = ['$scope', 'FormSchemaService'];

function MyController($scope, formSchemaService) {
    // using the already configured formSchemaService
    formSchemaService.buildForm(); 

So far this is pure angular and javascript service oriented programming. But the legacy integration comes here :

<script type="text/javascript">

   (function(app){
        var conf = app.conf = {
       'fields': {
          'field1: { // field configuration }
        }
     } ; 

     app.dispatchEvent(new Event('register-schema'));

 })(window);
</script>

Obviously every approach has it's merits and drawbacks. The advantages and use of this approach depends on your UI. The previously suggested approaches don't work in my case since my form schema and legacy code have no control and knowledge of angular scopes. Hence configuring my app based on angular.element('element-X').scope(); could potentially break the app if we change the scopes around. But if you're app has knowledge of the scoping and can rely on it not changing often, what's suggested previously is a viable approach.

Hope this helps. Any feedback is also welcome.

Casserole