Gets the context in which an event was fired.
An event's context contains information about the circumstances
surrounding the firing of the event.
The context property only appears in events on repeated elements.
You can use the event context with $w.at() to get a
selector function which selects items from a specific repeater item.
It contains an object with one key:value pair. The key is "itemId" and
the value is the ID of the repeated item on which the event occurred.