Convert firestore admin timestamp to date in javascript/nodejs/nextjs

Recently I was working on a Nextjs project where I was using @google-cloud/firestore package to write and read data from firestore.

I had createdAt and updatedAt timestamps inside documents which I wanted to convert to data object on the frontend.

Since timestapms created using server side firestore package (@google-cloud/firestore or firebase-admin/firestore) timestamps containes "_" prefix with seconds and nanoseconds keys

{ _seconds: 1700832176, _nanoseconds: 968000000 }

and if we try to convert this timestamp to date on frontend it gives error.

TypeError: user.updatedAt.toDate is not a function

To fix this error you have to convert this timestamp to date object on the server. for example in Nextjs api route.

import { NextResponse } from "next/server";
import { db } from "./database";


export async function GET(req: Request) {

  try {
    const collectionRef = db
    .collection("users")

  const snapshot = await collectionRef.get();
  const users = snapshot.docs.map((doc) => {
    const data = doc.data();
    return {
      id: doc.id,
      ...data,
      updatedAt: data.updatedAt.toDate(),
      appointmentAt: data.appointmentAt.toDate(),
    };
  });
  return NextResponse.json(appointments);

  } catch (error) {
    return NextResponse.json(error, {status: // status you want send })
  }
}