App.js

  componentDidMount() {
    this.askNotificationPermission();
  }

  askNotificationPermission = async () => {
    // check if the browser supports notifications
    if ("Notification" in window) {
      if (this.checkNotificationPromise()) {
        const permission = await Notification.requestPermission();
        this.handlePermission(permission);
      } else {
        Notification.requestPermission(permission => {
          this.handlePermission(permission);
        });
      }
    } else {
      console.log("This browser does not support notifications.");
    }
  };

  handlePermission = permission => {
    if (!("permission" in Notification)) {
      Notification.permission = permission;
    }
  };