Possible ordering dependency with `firebase-query` attached handler

[43081j]

For example:

<firebase-query path="/test" data="{{test}}"></firebase-query>

Steps to reproduce

• Load a page with a firebase-query in a background tab
• Switch to the tab
• Notice the query's data is empty

Why?

If you load this in an unfocused (background) tab in your browser, the query will be setup correctly and the data will be populated as expected (child_added events are fired).

If you then focus the tab in your browser, the first requested animation frame is processed, so Polymer calls any attached handlers. This triggers __queryChanged which will set the data to [].

The problem here seems to be that, because we already got the initial child_added events, they will not fire again and we will keep our empty array.

Not sure how we should deal with this, being more careful around the attached event somehow.

Expected behaviour

• child_added events fire
• data is populated
• tab is focused
• data remains populated

Actual behaviour

• child_added events fire
• data is populated
• tab is focused
• data is set to []
• child_added events don't fire again, data remains []

[tjmonsi]

@43081j Is this still happening? If it is not, we'll close this issue by next week