This event is emitted when AJAX requests are taking long to finish loading.
By default Unpoly will wait 400 ms for an AJAX request to finish
before emitting up:network:late
. You may globally,
for individual links or specific requests.
Once all responses have been received, an up:network:recover
will be emitted.
If additional requests are made while Unpoly is already busy waiting,
no additional up:network:late
events will be emitted.
By default, Unpoly will show a Progress bar while late requests are pending. You can disable the progress bar or implement custom loading indicators.