text: function getStartDate(state) {
      /*
      compute the startDate
      */
      const userData = state["userData"];
      let startDate = null;
      /*
      iterate date from today to back
      find the start of the most recend Period date
      whitch is the startDate
      */
      for (const date of Object.keys(userData).sort()) {
          if (userData[date]["Blood"] === 0) { 
          // not in period
              if (startDate !== null) {
                  return startDate;
              } 
          // if it is none, continue to find the most recend period date    
          } else {    
          // in period, update startDate
              startDate = date;
          }
      }
  }
  
  export default getStartDate;