const getEmails = (eventType) => {
    const usersRef = firebase.database().ref("users");
    let emailList = [];
    usersRef.once('value').then(function(dataSnapshot){
        let users = dataSnapshot.val();
        for(let user in users){
            if(users[user]['interestedEvents'][eventType]){
                emailList.push(users[user].email);
            }
        }
    });
    return emailList.toString();
}