Javascript Firebase web断开连接和mysql用户状态更改

当用户在firebase中脱机时，我如何更改mysql中该用户的状态

    const database = firebase.database();

    var myConnectionsRef = database.ref('onlineuser/'+userid+'/connections');

    var lastOnlineRef = database.ref('onlineuser/'+userid+'/lastOnline');

    var connectedRef = database.ref('.info/connected');
    connectedRef.on('value', function(snap) {
        if (snap.val() === true) {

            var con = myConnectionsRef.push();

            con.onDisconnect().remove();

            con.set(true);
            lastOnlineRef.onDisconnect().set(firebase.database.ServerValue.TIMESTAMP);
        }
    });