GoogleMapで複数ポイントを出し方 #JavaScript

GoogleMapで複数ポイントを出しクリックするとWindowがでるやり方。

GoogleDeveloperサイトより、修正しました。
単品のサンプルしかなかったので、複数試してみました。（どっかあるのかな・・・）
できるか確認なので、本来はループ等使用して使うん感じかなと思う。

<!DOCTYPE html>
<html>
  <head>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no">
    <meta charset="utf-8">
    <title>Info windows</title>
    <style>
      html, body {
        height: 100%;
        margin: 0;
        padding: 0;
      }
      #map {
        height: 100%;
      }
    </style>
  </head>
  <body>
    <div id="map"></div>
    <script>

// This example displays a marker at the center of Australia.
// When the user clicks the marker, an info window opens.

function initMap() {
  var uluru = {lat: -25.363, lng: 131.044};
  var map = new google.maps.Map(document.getElementById('map'), {
    zoom: 4,
    center: uluru
  });

  var contentString = '<div id="content">'+
      '<div id="siteNotice">'+
      '</div>'+
      '<h1 id="firstHeading" class="firstHeading">Uluru</h1>'+
      '<div id="bodyContent">'+
      '<p><b>Uluru</b>, also referred to as <b>Ayers Rock</b>, is a large ' +
      'sandstone rock formation in the southern part of the '+
      'Northern Territory, central Australia. It lies 335&#160;km (208&#160;mi) '+
      'south west of the nearest large town, Alice Springs; 450&#160;km '+
      '(280&#160;mi) by road. Kata Tjuta and Uluru are the two major '+
      'features of the Uluru - Kata Tjuta National Park. Uluru is '+
      'sacred to the Pitjantjatjara and Yankunytjatjara, the '+
      'Aboriginal people of the area. It has many springs, waterholes, '+
      'rock caves and ancient paintings. Uluru is listed as a World '+
      'Heritage Site.</p>'+
      '<p>Attribution: Uluru, <a href="https://en.wikipedia.org/w/index.php?title=Uluru&oldid=297882194">'+
      'https://en.wikipedia.org/w/index.php?title=Uluru</a> '+
      '(last visited June 22, 2009).</p>'+
      '</div>'+
      '</div>';

  var infowindow = new google.maps.InfoWindow({
    content: contentString
  });

  var marker = new google.maps.Marker({
    position: uluru,
    map: map,
    title: 'Uluru (Ayers Rock)'
  });
  marker.addListener('click', function() {
    infowindow.open(map, marker);
  });

  var marker2 = new google.maps.Marker({
    position: {lat: -25.300, lng: 131.044},
    map: map,
    title: 'Uluru (Ayers Rock)'
  });
  marker2.addListener('click', function() {
    infowindow.open(map, marker2);
  });

}

    </script>
    <script async defer
        src="https://maps.googleapis.com/maps/api/js?key=YOUR_KEY&signed_in=true&callback=initMap"></script>
  </body>
</html>