Add hasListeners method to EventEmitter

[mjethani]

Background

The extension contains a hasListener(tabId) method in lib/hitLogger.js. This should be done by Core instead, in lib/events.js, by keeping track of whether an event has any listeners. Most of the time the HitLogger object in the extension does not have any listeners for any events, therefore this could be optimized in Core to avoid a lookup in the internal _listeners map, simply by checking the value of its size property first.

What to change

In lib/events.js modify EventEmitter.prototype.off to remove any entry that has no listeners left.

Add a new method hasListeners(name) that returns true if there are any filters for the given event or, if no name is given, for any event.

Integration notes

The extension should modify its lib/hitLogger.js to redefine the hasListener method as follows:

function hasListener(tabId)
{
  return eventEmitter.hasListeners(tabId);
}

Hints

The new hasListener method is not used by the extension as of now. Please see the dependency update ticket for this change for hints on how to test this.

[sebastian]

Thanks for filing this issue, and sorry for the confusion, but I ​don't think we need that after all.

[mjethani]

Thanks for the clarification.

As I mentioned in the description, we could still use this because right now the extension is accessing the internal property _listeners. But we don't need to make any more changes, just call eventEmitter.hasListeners() in lib/hitLogger.js.

[abpbot]

A commit referencing this issue has landed:
​Issue 7202 - Add hasListeners method to EventEmitter

[abpbot]

A commit referencing this issue has landed:
​Issue 7202 - Add hasListeners method to EventEmitter