Is there a way to check for closed window AddThis with event listener?

Is there a way to check for closed window AddThis with event listener?

I am using some API functionality with AddThis. I found an API example
that will create an alert box when AddThis fully loads on the page. Is
there another event listener that I can use to create a popup box after a
person closes one of the sharing popup windows? Basically I want to check
and see if the AddThis popup window is closed, then trigger another alert
box after that. I will post the example and the link to the reference for
the API. I do not understand javascript event listeners very well so I
apologize for any ignorance in advance.
link to API documentation for AddThis:
http://support.addthis.com/customer/portal/articles/381263-addthis-client-api#events-types
the example used:
function addthisReady(evt) {
alert('AddThis API is fully loaded.');
}
addthis.addEventListener('addthis.ready', addthisReady);