Cannot use import statement outside a module (Vanilla JS)

I’m getting Cannot use import statement outside a module(Vanilla Javascript) while testing a simple demo app locally using nano server.

data.js

const data = {
    "type": "Feature",
    "properties": {
        "name": "Coors Field",
        "amenity": "Baseball Stadium",
        "popupContent": "This is where the Rockies play!"
    },
    "geometry": {
        "type": "Point",
        "coordinates": [-104.99404, 39.75621]
    }
}

export {data};

index.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Supercluster Leaflet demo</title>

        <link rel="stylesheet" href="https://unpkg.com/[email protected]/dist/leaflet.css" integrity="sha256-kLaT2GOSpHechhsozzB+flnD+zUyjE2LlfWPgU04xyI=" crossorigin="" />
        <script src="https://unpkg.com/[email protected]/dist/leaflet.js" integrity="sha256-WBkoXOwTeyKclOHuWtc+i2uENFpDZ9YPdf5Hf+D7ewM=" crossorigin=""></script>

        <link rel="stylesheet" href="cluster.css" />

        <style>
            html, body, #map {
                height: 100%;
                margin: 0;
            }
        </style>
    </head>
    <body>
        <div id="map"></div>
        <script type="module" src="data.js"></script>
        <script src="index.js"></script>
    </body>
</html>

index.js

import {data} from 'data.js';

/*global L */

// The rest not needed