logEvent listener.js

var impression_count = 0;
var count_impressions = function(logEvent){
	var visitors = logEvent.params.visitors;
	visitors.forEach(function(visitor){
		console.log(visitor)
		var snapshots = visitor.snapshots;
		snapshots.forEach(function(snapshot){
			var events = snapshot.events
			events.forEach(function(event){
				if(event.key == "campaign_activated"){
					console.log(event.entity_id);
					impression_count++
					console.log(impression_count);
				}

			})
		});
		})
}