Subscription

Subscription object is returned by Chart Methods. Using this object you can subscribe to a chart event and unsubscribe from it. So it has two methods:

###subscribe(object, method, singleshot)

1. object is a context to be used as this pointer for method function. Use null if you don't need the context.
2. method is a function to be called when the event happens
3. singleshot is an optional argument. Set it to true to be automatically unsubscribed when the event happens first time.

###unsubscribe(object, method)

Use the same object and method which you used in subscribe function to unsubscribe from the event.