Leaking window.__powerCalendars

[apellerano-pw]

The code currently creates a window.__powerCalendars hash, and fills it as you create more instances of power-calendar.

However if the last instance of power-calendar is destroyed, it will still leave an empty hash. The unregisterCalendar hook could check Object.keys(window.__powerCalendars).length and delete the property from window if there are no more entries.

This would prevent power-calendar from tripping QUnit's useful "Check for Globals" feature, which detects global state leaks like this.

Any code checking the hash will also need to first check that the hash exists.

[mkszepp]

@apellerano-pw thanks for reporting.

Would you like to make a PR to fix this issue?

[apellerano-pw]

Here's one #543

I tested by running the test-app's QUnit suite in browser, and observed that __powerCalendars is no longer in the list of leaked objects

[mkszepp]

fixed by #543