How to update a specific data in Firebase (with ionic)

When I click the button, I want you to add +1 to the count, as if it were a reputation, every +1 click on the Firebase field, but when I click it it appears [object] [object] 1

This is my code:

constructor(public navCtrl: NavController, public navParams: NavParams, public alertCtrl: AlertController, public db: AngularFirestore) {

this.id = navParams.get("id")
this.pessoa = db.collection<any>("usuarios", ref => ref.where("id", "==", this.id)).valueChanges();

this.contadorPositivo = db.collection<any>("usuarios", ref => ref.where("contadorPositivo", "==", this.id)).valueChanges();
this.contadorNegativo = db.collection<any>("usuarios").valueChanges();
console.log(this.contadorNegativo.value);
}

votoNegativo() {
    console.log(this.contadorNegativo);
    this.db.collection('usuarios/').doc(this.id).update({contadorNegativo: + 1});
    const alert = this.alertCtrl.create({
      title: '',
      subTitle: 'Obrigado pela classificação!',
      buttons: [
        {
          text: 'OK',
          handler: data => {
            this.navCtrl.pop();
          }
        }
      ]
    });
    alert.present();
  }
    votoPositivo() {
      this.db.collection('usuarios').doc(this.id).update({contadorNegativo: + 1});
      const alert = this.alertCtrl.create({
        title: '',
        subTitle: 'Obrigado pela classificação!',
        buttons: [
          {
            text: 'OK',
            handler: data => {
              this.navCtrl.pop();
            }
          }
        ]
      });
      alert.present();
  }

}