How to get location coordinates knowing place_id via google javascript api

From the example in the Google Maps Javascript API v3 documentation (with your place_id):

var infowindow = new google.maps.InfoWindow();
var service = new google.maps.places.PlacesService(map);

service.getDetails(request, function(place, status) {
  if (status == google.maps.places.PlacesServiceStatus.OK) {
    var marker = new google.maps.Marker({
      map: map,
      position: place.geometry.location
    });
    google.maps.event.addListener(marker, 'click', function() {
      infowindow.setContent(place.name);
      infowindow.open(map, this);
    });
    map.fitBounds(place.geometry.viewport);
  }
});

working fiddle

code snippet:

var geocoder;
var map;

function initialize() {
  var map = new google.maps.Map(
    document.getElementById("map_canvas"), {
      center: new google.maps.LatLng(37.4419, -122.1419),
      zoom: 13,
      mapTypeId: google.maps.MapTypeId.ROADMAP
    });
  var request = {
    placeId: 'ChIJOwE7_GTtwokRFq0uOwLSE9g'
  };

  var infowindow = new google.maps.InfoWindow();
  var service = new google.maps.places.PlacesService(map);

  service.getDetails(request, function(place, status) {
    if (status == google.maps.places.PlacesServiceStatus.OK) {
      var marker = new google.maps.Marker({
        map: map,
        position: place.geometry.location
      });
      google.maps.event.addListener(marker, 'click', function() {
        infowindow.setContent(place.name);
        infowindow.open(map, this);
      });
      map.fitBounds(place.geometry.viewport);
    }
  });

}
google.maps.event.addDomListener(window, "load", initialize);

html,
body,
#map_canvas {
  height: 100%;
  width: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://maps.googleapis.com/maps/api/js?libraries=places&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map_canvas" style="border: 2px solid #3872ac;"></div>

You don't need a map. It is a Restful web service that returns a JSON string. In your application, you only need to send a HTTP request to

GET https://maps.googleapis.com/maps/api/geocode/json?place_id=ChIJOwE7_GTtwokRFq0uOwLSE9g&key=KEY_GOES_HERE

and then parse the JSON string returned, and retrieve the latlng inside.

If you are using Jquery in your web app, you may do

    $.ajax({
            type: "GET",
            url: "https://maps.googleapis.com/maps/api/geocode/json?place_id=ChIJOwE7_GTtwokRFq0uOwLSE9g&key=KEY_GOES_HERE",
            dataType: "text", 
            success: function (yourJSONstring){
                var respJson = $.parseJSON(yourJSONstring);  

            // then something like ... 
            // respJson.results[0].geometry.location.lat;
            // respJson.results[0].geometry.location.lng; 


            },
            error: function (xhr) {
            }
        });