Why do we use rootScope broadcast in AngularJS

Question

Tried to find some basic information for AngularJS  rootScope  broadcast  But the AngularJS documentation doesn t help much  In easy words why do we use this   Also  inside John Papa s Hot Towel template there is a custom function in the common module named  broadcast   function  broadcast         return  rootScope  broadcast apply  rootScope  arguments       I did not understand what this is doing  So here are couple of basic questions   1  What does  rootScope  broadcast do   2  What is the difference between  rootScope  broadcast and  rootScope  broadcast apply

User · Answer

What does  rootScope  broadcast do   It broadcasts the message to respective listeners all over the angular app  a very powerful means to transfer messages to scopes at different hierarchical level be it parent   child or siblings   Similarly  we have  rootScope  emit  the only difference is the former is also caught by  scope  on while the latter is caught by only  rootScope  on    refer for examples  - http   toddmotto com all-about-angulars-emit-broadcast-on-publish-subscribing

User · Answer

rootScope  broadcast is a convenient way to raise a  global  event which all child scopes can listen for   You only need to use  rootScope to broadcast the message  since all the descendant scopes can listen for it      The root scope broadcasts the event    rootScope  broadcast  myEvent      Any child Scope can listen for the event    scope  on  myEvent  function     console log  my event occurred          Why we use  rootScope  broadcast  You can use  watch to listen for variable changes and execute functions when the variable state changes  However  in some cases  you simply want to raise an event that other parts of the application can listen for  regardless of any change in scope variable state   This is when  broadcast is helpful

User · Answer

What does  rootScope  broadcast do    rootScope  broadcast is sending an event through the application scope  Any children scope of that app can catch it using a simple   scope  on     It is especially useful to send events when you want to reach a scope that is not a direct parent  A branch of a parent for example       One thing to not do however is to use  rootScope  on from a controller   rootScope is the application  when your controller is destroyed that event listener will still exist  and when your controller will be created again  it will just pile up more event listeners   So one broadcast will be caught multiple times   Use  scope  on   instead  and the listeners will also get destroyed  What is the difference between  rootScope  broadcast  amp   rootScope  broadcast apply   Sometimes you have to use apply    especially when working with directives and other JS libraries  However since I don t know that code base  I wouldn t be able to tell if that s the case here

User · Answer

Passing data      I wonder why no one mention that  broadcast accept a parameter where you can pass an Object that will be received by   on using a callback function  Example      the object to transfert var myObject         status   10     rootScope  broadcast  status updated   myObject        scope  on  status updated   function event  obj       console log obj status      10

User · Answer

rootScope basically functions as an event listener and dispatcher   To answer the question of how it is used  it used in conjunction with rootScope  on    rootScope  broadcast  hi      rootScope  on  hi   function          do something       However  it is a bad practice to use  rootScope as your own app s general event service  since you will quickly end up in a situation where every app depends on  rootScope  and you do not know what components are listening to what events   The best practice is to create a service for each custom event you want to listen to or broadcast    service  hiEventService  function  rootScope        this broadcast   function     rootScope  broadcast  hi        this listen   function callback    rootScope  on  hi  callback

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