Convert string to JSON data in Angular

Hi,

I have this code where I need to send something in json formate to my api server: 

 subscribeEmail()
  {
    // convert theEmail string to json?
    const theEmail = localStorage.getItem("email");

    const httpOptions = {
      headers: new HttpHeaders({
        Authorization: 'Bearer ' + sessionStorage.getItem('accessToken')
      })
    };
      return this.http.post(this.baseUrl + '/message/save' + theEmail , httpOptions);   
  }

I need to send theEmail variable as json format, how to do that?