位置情報

読み取り専用のNavigator.geolocationは、ウェブコンテンツがデバイスの位置情報にアクセスするためのGeolocationオブジェクトを返す。


<!DOCTYPE html>
<html>
  <head>
    <title>Simple Map</title>
    <meta name="viewport" content="initial-scale=1.0">
    <meta charset="utf-8">
    <style>
      #map {
        height: 50%;
        margin-top: 10px;
      }
      html, body {
        height: 100%;
        margin: 10px;
        padding: 0;
      }
    </style>
  </head>
  <body>
  	<div id="map"></div>
  	<script>


      function initMap() {
        var map = new google.maps.Map(document.getElementById('map'), {
          center: {lat: -34.397, lng: 150.644},
          zoom: 2
        });
        var infoWindow = new google.maps.InfoWindow({map: map});

        if (navigator.geolocation) {
          navigator.geolocation.getCurrentPosition(function(position) {
            var pos = {
              lat: position.coords.latitude,
              lng: position.coords.longitude
            };

            infoWindow.setPosition(pos);
            infoWindow.setContent('Location found.');
            map.setCenter(pos);
          }, function() {
            handleLocationError(true, infoWindow, map.getCenter());
          });
        } else {
          handleLocationError(false, infoWindow, map.getCenter());
        }
      }

      function handleLocationError(browserHasGeolocation, infoWindow, pos) {
        infoWindow.setPosition(pos);
        infoWindow.setContent(browserHasGeolocation ?
                              'Error: The Geolocation service failed.' :
                              'Error: Your browser doesn\'t support geolocation.');
      }
    </script>
  	<script async defer
src="https://maps.googleapis.com/maps/api/js?key=&callback=initMap">
</script>
</body>
</html>

一通り終わったと思ったらこれか？
なるほど、navigator.geolocation.getCurrentPositionで位置情報を取得していますね。

<script>

var options = {
	enableHighAccuracy : true,
	timeout: 5000,
	maximumAge: 0
};

function success(pos){
	var crd = pos.coords;

	console.log('your current position is:');
	console.log('latitude : ' + crd.latitude);
	console.log('longitude: ' + crd.longitude);
	console.log('More or less ' + crd.accuracy + ' meters');
};

function error(err){
	console.warn('ERROR(' + err.code + '):' + err.message);
};

navigator.geolocation.getCurrentPosition(success, error, options);
</script>