How can I convert image buffer to string base64?

I am uploading image using Filepond library to MongoDB using Mongoose. I want to show the image in the map’s marker using pop-up feature. Image I am getting back in the format

{ location:
   { type: 'Point',
     coordinates: [ -86.34164, 39.81514 ],
     formattedAddress: 'Lucas Oil Raceway, Brownsburg, IN 46234, US' },
  _id: 5f10a1867435d3f048a14acc,
  storeId: '009',
  dateCompleted: 2020-07-01T04:00:00.000Z,
  description:
   ' setup datguard. backups, flashack logs  and monitoring',
  createdAt: 2020-07-16T18:50:46.997Z,
  storeImage:
   Binary {
     _bsontype: 'Binary',
     sub_type: 0,
     position: 3569671,
     buffer:
      <Buffer ff d8 ff e0 00 10 4a....
storeImageType: 'image/jpeg',
  __v: 0 }

I am able to show rest of the properties except image. Is there a way i can convert this image buffer to string and then set to map properties.

stores = data.data.map(store => {
        return {
            type: 'Feature',
            geometry: {
                type: 'Point',
                coordinates: [
                    store.location.coordinates[0],
                    store.location.coordinates[1]
                ]
            },
            properties: {
                storeId: store.storeId,
                dateCompleted: store.dateCompleted,
                description: store.description,
                         
          image:`data:${store.storeImageType};charset=utf-8;base64,${store.storeImage.data.toString('base64')}`,

##with this i see image content as "data:image/jpeg;charset=utf;base64,233,4444,555,67
icon: ‘shop’
}
};
});

function setMarkers(stores) {
    //add markers to the map
    stores.forEach(function (marker) {

        // create a HTML element for each feature
        var el = document.createElement('div-marker');
        el.className = 'marker';

        // make a marker for each feature and add to the map
        var mkr = new mapboxgl.Marker(el)
            .setLngLat(marker.geometry.coordinates)
            .setPopup(new mapboxgl.Popup({
                    offset: 25
                }) // add popups this is where i need to set image
                .setHTML("<img src='" + marker.properties.image + "' width='160' />"))
            .addTo(map);
        mkrs.push(mkr);
    });
}

All this code is in public javascript folder using NodeJS Express.