Conditional EventListener

Issue

I was just wondering if there is a way to define conditional event listener i.e. is there a way to listen for the event only if some condition is met.

I think I am asking for an unorthodox stuff, or there is a way already exists which I am oblivious of.

Example:

Let 'lastRepeat' be an event emitted by the directive when ng-repeat ends.

app.controller('ctrl',function($scope){
  $scope.$on('lastRepeat', callback);  // Here the callback will be called every time lastRepeat event is emitted by the directive 
});

But what I am looking for is something like this (This is what I have thought of, solution need not use same approach):

app.controller('ctrl',function($scope){
  function foo(){
    if(bool)
      $scope.$on('lastRepeat', callback); // Problem listening like this is that a listener is created everytime foo is called and condition is met and hence we end up having multiple listeners
  }
)};

Basically I want to avoid this multiple creation of listeners. Is there a way I can store this listener like a variable and listen only if some condition is met.

Solution

How about:

app.controller('ctrl', function($scope) {

  var condition = false;
  var callback = function () {};

  $scope.$on('lastRepeat', function() {
    if (!condition) return;
    callback();    
  });
});

Answered By - tasseKATT