Loading external GeoJSON (Promise Method): Boilerplate

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>Starter map</title>
    <meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
    <link rel="stylesheet" href="https://unpkg.com/leaflet@1.0.3/dist/leaflet.css" />
    <style>
        body {
            margin: 0;
            padding: 0;
        }
        #map {
            position: absolute;
            top: 0;
            bottom: 0;
            width: 100%;
        }
    </style>
</head>

<body>
    <div id="map"></div>
    <script src="https://unpkg.com/leaflet@1.0.3/dist/leaflet.js"></script>
    <script>
        var map = L.map('map')
            .setView([37.857507, -85.632935], 7);

</html>

https://unpkg.com/leaflet@1.0.3/dist/leaflet.js