How to get current user address from firebase console

  currentUserId: any;
  currentadd: FirebaseListObservable<any>;
openMapPage()
  {
    var ref = firebase.database().ref("request");
    ref.once("value").then((snapshot) => { // <------ Here!
        var a = snapshot.exists();  // true
        var c = snapshot.hasChild("reqdetails"); // true
        var d = snapshot.child('reqdetails').exists();
        var requestsKey = snapshot.key;
        var requestsValue = snapshot.val();
       
        
          this.currentadd = this.currentUserId.regdetails.address;
          console.log("Current User Address");
          console.log(this.currentadd);
      
        snapshot.forEach((childSnapshot) => { // <------ And here!
            var requestKey = childSnapshot.key;
            var requestValue = childSnapshot.val();
            var reqdetails = requestValue.reqdetails;
            var AllUserAddress = requestValue.regdetails.address;
            
           
           //var currentUserAdd = currentUserId.address;
            if (reqdetails) {
                this.data = requestKey;
                console.log(this.data);
                //this.arr.push(requestKey);
                //console.log(this.arr);
              
                 this.getRequest = this.angFire.list('request', {
                   query: {
                   orderByChild: 'reqdetails',
                   startAt: 'reqdetails'
            }
         }) 
            }
        });

    });     
  }

I am getting this error when i do console.log(this.currentadd);.