signInUser(email: string, password: string) {
    return new Promise(
      (resolve, reject) => {
        firebase.auth().signInWithEmailAndPassword(email, password).then(
          () => {
            this.setOnlineState(true);
            resolve();
          },
          (error) => {
            reject(error);
          }
        );
      }
    );
  }

  signOutUser() {
    this.setOnlineState(false);
    firebase.auth().signOut();
  }

  setOnlineState(state: boolean) {
    const currentUser = firebase.auth().currentUser;
    firebase.database().ref("users/" + currentUser.uid).update({ onlineState: state });
  }

window.onbeforeunload :  (e) => {
       this.setOnlineState(false);
    };