Enabling CORS in Cloud Functions for Firebase

You can set the CORS in the cloud function like this

response.set('Access-Control-Allow-Origin', '*');

No need to import the cors package

There are two sample functions provided by the Firebase team that demonstrate the use of CORS:

• Time server with date formatting
• HTTPS endpoint requiring Authentication

The second sample uses a different way of working with cors than you're currently using.

Consider importing like this, as shown in the samples:

const cors = require('cors')({origin: true});

And the general form of your function will be like this:

exports.fn = functions.https.onRequest((req, res) => {
    cors(req, res, () => {
        // your function body here - use the provided req and res from cors
    })
});