How do I get the server timestamp in Cloud Functions for Firebase?

If you use the Firebase Admin SDK, here is the correct syntax (Checked 2019-08-27):

const admin = require('firebase-admin');
// or
// import * as admin from 'firebase-admin';

// Using Cloud Firestore
admin.firestore.FieldValue.serverTimestamp()

// Using Realtime Database
admin.database.ServerValue.TIMESTAMP

Since you're already using the admin SDK, the correct syntax is:

admin.database.ServerValue.TIMESTAMP

I'm new to node.js myself, but Date.now() works in my tests.

Edit

I misunderstood you question--didn't realize you wanted to timestamp data you were storing in the Firebase database. I thought you simply wanted to get the time on the server that was running your cloud function. If you want to timestamp a received email being stored in the Firebase database, then using admin.database.ServerValue.TIMESTAMP is without question the best approach.

Just for my own education, I wrote the following function to see how the times compare. I would expect the times on the cloud function server and database server are synced to a very accurate time reference. When I run this function, the database timestamp typically within a hundred milliseconds of the Date.now() value. The database timestamp being a little later is reasonable, given that it takes the cloud function some time to connect to the database and perform the write.

exports.timeTest = functions.database.ref('/test/trigger')
    .onWrite(event => {

        const now= Date.now();
        console.log('now=', now);

        const timeVals = {
          dateNow : now,
          serverTimestamp : admin.database.ServerValue.TIMESTAMP
        };

        return event.data.ref.parent.child('times').update(timeVals);
    });

Just to clarify for future readers:

admin.database.ServerValue.TIMESTAMP returns a non-null Object and is a placeholder value for auto-populating the current timestamp. It doesn't contain the actual timestamp. The database will replace this placeholder when it will execute the command.

If you are using it inside a database.ref then it works just as you expect and is the preferred way to enter a timestamp :

var sessionsRef = firebase.database().ref("sessions");
sessionsRef.push({
startedAt: firebase.database.ServerValue.TIMESTAMP // this will write 'startedAt: 1537806936331`
});

But if you try to use it outside the database function (for example to return the time now or make some calculations) it will return an object that you cannot use it:

console.log(firebase.database.ServerValue.TIMESTAMP) // this will return an [object Object]

See more about it in firebase.database.ServerValue and in this SO question.

Date.now() works just fine outside a database function if you want to use it for a calculation or any other general use.

console.log(Date.now()); // this will return 1537806936331

Both of them are using unix time which is number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, and it is irrelevant from the timezone. It is the same number on client and on server (...or almost:-). See unix time .