deleting whole flatlist in one go using firestore 

filter data=(_item)=>{
   this.setState({users: this.state.users.filter(item => item. Key=== _item)});
    console.log(this.state.favorites) }
call this function in button deleteall code given below
  {   async function massDeleteUsers() {
              // Get all users
              const usersQuerySnapshot = await firestore().collection('user').get(                 
              );             
              // Create a new batch instance
              const batch = firestore().batch();             
              usersQuerySnapshot.forEach(documentSnapshot => {
                batch.delete(documentSnapshot.ref); });             
              return batch.commit();}             
           massDeleteUsers().then(() =>{     
             this.filterdata()
               console.log('All users deleted in a single batch operation.')}) }}>
so this will delete whole flatlist in on go and delete whole firestore collection