Retrieving a date from Firestore in Node.js - node.js

Question

From the Firestore documentation on saving data of supported types, I red:
var docData = {
//...
dateExample: new Date("December 10, 1815"),
//...
}
};
db.collection("data").doc("one").set(docData).then(function() {
console.log("Document successfully written!");
});
This is what I use in my Cloud Functions to save various dates to Firestore.
It works great !
My problem comes when I need to retrieve those dates and post them as String to a third party API.
As far as I understood, in Firebase/Firestore, dates are stored as a Unix Timestamp.
I couldn't find anywhere (firebase doc, stackoverflow ...) how to convert it properly to a String.
I tried unsuccessfully the following:
function timeConverter(UNIX_timestamp){
var a = new Date(UNIX_timestamp * 1000);
var months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];
var year = a.getFullYear();
var month = months[a.getMonth()];
var date = a.getDate();
var hour = a.getHours();
var min = a.getMinutes();
var sec = a.getSeconds();
var time = date + ' ' + month + ' ' + year + ' ' + hour + ':' + min + ':' + sec ;
return time;
}
admin.firestore().collection('users').doc(userId).get()
.then( (doc) => {
const user = doc.data();
const birthDate = user.birthDate;
const birthDateString = timeConverter(birthDate);
console.log(`birthDateString =${birthDateString}`);
// "birthDateString = NaN undefined NaN NaN:NaN:NaN"
});

Answer 1

First you can use toDate() to convert the Firebase timestamp to a Date object and then use the Date's object method toDateString() to convert it to a String.
const birthDate = user.birthDate.toDate();
const birthDateString = birthDate.toDateString();
You can also check out Moment.js, it helps a lot when dealing with Dates and displaying them.

Answer 2

This boils down to : how do I convert a unix timestamp to a human readable date?
There are several ways to do this but one of the easiest is to use
var readableData = new Date(doc.data().myUnixTimestamp).toLocaleDateString("en-US");
There are options for all locales. See MDN's Date.prototype.toLocaleDateString.