Push data in array but after converting timestamp to date

Issue

Fetching data from Firestore and pushing it into an array. This is working fine but in this process I am changing timestamp format and I want this value of timestamp in my array and not the original one. How do I replace this value from original and push ?

My code so far:

home.ts

firebase.firestore().collection("dailyreport").where("timestamp", ">=", start)
    .onSnapshot(querySnapshot => {
        var cities = [];
        querySnapshot.forEach( doc=> {

  const timeinmillsecs = doc.data().timestamp.seconds * 1000; 
  let a1 = new Date(timeinmillsecs); 
  let show_year_month_date =  a1.getFullYear()+'/'+(a1.getMonth()+1) +'/'+a1.getDate(); // 3.convert to imple date

  console.log(show_year_month_date); // ***NEED THIS VALUE IN dailyreports ARRAY 

         this.dailyreports.push(doc.data());
         console.log("Timestamp greather than 29march -- ", (doc.data()));
        });
    });

The screenshot of console.log(doc.data())

Edit 1

Before pushing, I have assigned value like this -

doc.data().timestamp = show_year_month_date;
this.dailyreports.push(doc.data());

But it is also not working.

Edit 2

Screenshot of dailyreports and doc:

Solution

Instead of trying to update doc.data(), copy the value to a new variable say data. Update the timestamp in data and then push data to this.dailyreports. And then console log data to see the object with updated timestamp that was pushed to this.dailyreports.

firebase.firestore().collection("dailyreport").where("timestamp", ">=", start)
  .onSnapshot(querySnapshot => {
    var cities = [];
    querySnapshot.forEach(doc => {
      const data = doc.data();

      const timeinmillsecs = data.timestamp.seconds * 1000;
      let a1 = new Date(timeinmillsecs);
      let show_year_month_date = a1.getFullYear() + '/' + (a1.getMonth() + 1) + '/' + a1.getDate(); // 3.convert to imple date

      data.timestamp = show_year_month_date;
      console.log(show_year_month_date); // ***NEED THIS VALUE IN dailyreports ARRAY 
      


      this.dailyreports.push(data);
      console.log("Timestamp greather than 29march -- ", data);
    });
  });

Answered By - abd995