This code is work for me
<script src="https://www.gstatic.com/firebasejs/4.5.1/firebase.js"></script>
<script>
var config = {
apiKey: "",
authDomain: "",
databaseURL: "",
projectId: "",
storageBucket: "",
messagingSenderId: ""
};
firebase.initializeApp(config);
var reff = firebase.database().ref('message');
reff.on('value',haveData, haveerr);
function haveData(datahave){
var existval= datahave.val();
var chabi=Object.keys(existval);
for(var d2=0;d2< chabi.length;d2++){
var r=chabi[d2];
var exitval=existval[r].Message;
var exitval1=existval[r].Name;
var exit=existval[r].Email;
var exitval2=existval[r].Subject;
var timestamp=existval[r].timestamp;
var sdate=new Date(timestamp);
var Year=sdate.getFullYear();
var month=sdate.getMonth()+1;
var day=sdate.getDate();
var hh=sdate.getHours();
var mm=sdate.getMinutes();
var ss=sdate.getSeconds();
}
}
function haveerr(e){
console.log(e);
}
</script>