[Zeppelin 1415] - Adding Zeppelin-Web Good Practice Guide #2

contribution/zeppelinweb/goodPracticeGuide01.md

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 layout: sideMenu
-title: "Defining Components"
+title: "1 - Defining Components"
 description: ""
 group: nav-contrib-front
 menu: nav-contrib-front

contribution/zeppelinweb/goodPracticeGuide02.md

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+---
+layout: sideMenu
+title: "2 - Event Dispatching"
+description: ""
+group: nav-contrib-front
+menu: nav-contrib-front
+---
+<!--
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+# Event Dispatching in Angular
+
+<br/>
+AngularJS provides an Event dispatching system allowing the communication between controllers or services and controllers.
+
+`$broadcast` dispatches the event downwards through the child scopes
+
+`$emit` dispatches the event upwards through the scope hierarchy
+
+`$on` catches the event passing by that scope
+
+<br/>
+You can usually see it being used from `$rootScope` or `$scope`
+
+```
+$scope.$broadcast('eventName', arg);
+$rootScope.$broadcast('eventName', arg);
+
+$scope.$emit('eventName', arg);
+$rootScope.$emit('eventName', arg);
+
+$scope.$on('eventToCatch', function);
+$rootScope.$on('eventToCatch', function);
+```
+
+Now, there are a few things to know about using it from `$rootScope`:
+
+* Both `$rootScope.$emit` and `$rootScope.$broadcast` go through child scopes since `$rootScope` doesn't have a parent
+* `$rootScope.$emit` can only be received by `$rootScope.$on`
+* `$rootScope.$broadcast` can be received by `$rootScope.$on` and `$scope.$on`
+* `$rootScope.$on` listener needs to be removed by hand (Memory leak if forgotten)
+
+
+#### How we are using it in the project
+
+* Usage of event dispatching should be limited if possible
+* We only use `$rootScope.$broadcast` and `$scope.$on` for event dispatching/catching
+
+
+#### Performances
+
+Using `$broadcast` might not seem optimum if we consider the description we have above.
+
+However, it is optimized to only go through branches that have a matching event binding.
+(cf. [this post](http://www.bennadel.com/blog/2724-scope-broadcast-is-surprisingly-efficient-in-angularjs.htm))