<!DOCTYPE html>

<html>
    <head>
        <style>

            html, body, #map
            {
                height: 100%;
                margin: 0;
            }

        </style>
        <title>map</title>
    </head>
    <body>
        <div id="map"></div>
        <script>

            function initMap() {
                var map = new google.maps.Map(document.getElementById('map'), {
                    center: {lat: 39.833, lng: -98.583},
                    zoom: 4
                });
                var marker = new google.maps.Marker({
                    map: map,
                    position: {lat: 42.3762, lng: -71.1158}
                });
                var marker = new google.maps.Marker({
                    map: map,
                    position: {lat: 41.3104, lng: -72.9289}
                });
            }

        </script>
        <script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBKMo-DfSUsW3LvS1C0xxKGOSX2A1HxNx4&callback=initMap"></script>
    </body>
</html>