A convenience object that simplifies the common pattern of attaching event listeners
to several events, then removing all those listeners at once later, for example, in
a destroy method.
Example:
const helper = new Cesium.EventHelper();
helper.add(someObject.event, listener1, this);
helper.add(otherObject.event, listener2, this);
// later...
helper.removeAll();
    
    
    
    
    
    See:
Methods
add(event, listener, scope) → EventHelper.RemoveCallback
    Adds a listener to an event, and records the registration to be cleaned up later.
    
| Name | Type | Description | 
|---|---|---|
event | 
            
            Event | The event to attach to. | 
listener | 
            
            function | The function to be executed when the event is raised. | 
scope | 
            
            object | 
            
                
                        optional
                
                
                
            
                An optional object scope to serve as the this
       pointer in which the listener function will execute. | 
        
Returns:
    A function that will remove this event listener when invoked.
    
        
            
    
    
    Unregisters all previously added listeners.
        
    
    
        Type Definitions
    A function that removes a listener.
