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InterestEvent
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The InterestEvent interface represents an event that fires when interest is shown or lost on an interest invoker.
This is the event object for the interest and loseinterest events, which fire on the target element when interest is shown or lost, respectively.
This interface inherits properties from its parent, Event.
InterestEvent.source Read only -
An Element object instance that represents the interest invoker element on which interest was shown or lost to fire the event.
This feature does not appear to be defined in any specification.