GoogleMaps ne se charge pas au chargement de la page

Je ne peux pas obtenir ma carte de course à l'aide de l'API GoogleMaps V3. La carte ne se charge pas. J'attendrais la carte apparaissent dans le div avec l'id gisMap mais dans le Chrome Débogueur, j'obtiens le message:

Uncaught InvalidValueError: initMap is not a function

Javascript

var map;

function initMap() {
    //Enabling new cartography and themes
    google.maps.visualRefresh = true;

    //Setting starting options
    var mapOptions = {
        center: new google.maps.LatLng(39.9078, 32.8252),
        zoom: 10,
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };

    //Getting Map DOM Element
    var mapElement = document.getElementById('gisMap');

    //Creating a map with DOM element
    map = new google.maps.Map(mapElement, mapOptions);
}

Bundle.js (extrait)

(...)
module.exports = Vue;
}).call(this,require('_process'))
},{"_process":1}],3:[function(require,module,exports){
'use strict';

var map;

function initMap() {
    //Enabling new cartography and themes
    google.maps.visualRefresh = true;

    //Setting starting options
    var mapOptions = {
        center: new google.maps.LatLng(39.9078, 32.8252),
        zoom: 10,
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };

    //Getting Map DOM Element
    var mapElement = document.getElementById('gisMap');

    //Creating a map with DOM element
    map = new google.maps.Map(mapElement, mapOptions);
}

},{}],4:[function(require,module,exports){
'use strict';

var Vue = require('vue');

new Vue({});
(...)

HTML

<!doctype html>
<html lang="en">

    <head>
    <meta charset="UTF-8">
    <title>MFServer Test</title>

    <link rel="stylesheet" href="/css/app.css">
</head>
    <nav class="navbar navbar-inverse navbar-fixed-top">
    <div class="container">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a class="navbar-brand" href="#">MFDispo</a>
        </div>
        <div id="navbar" class="collapse navbar-collapse">
            <ul class="nav navbar-nav">
                <li class="active"><a href="#">Start</a></li>
                <li><a href="#about">GIS</a></li>
            </ul>
        </div><!--/.nav-collapse -->
    </div>
</nav>

    <body id="app">
        <div class="pageWrapper">
            <div id="gisMap"></div>
            <div id="content"></div>
        </div>

        <script src="/js/bundle.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js" integrity="sha256-KXn5puMvxCw+dAYznun+drMdG1IFl3agK0p/pqT9KAo= sha512-2e8qq0ETcfWRI4HJBzQiA3UoyFk6tbNyG+qSaIBZLyW9Xf3sWZHN/lxe9fTh1U45DpPf07yj94KsUHHWe4Yk1A==" crossorigin="anonymous"></script>
<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBDucSpoWkWGH6n05GpjFLorktAzT1CuEc&callback=initMap" async defer></script>
    </body>

</html>

SCSS

@import "node_modules/bootstrap-sass/assets/stylesheets/bootstrap";
@import "partials/forms";

html, body {
  height: 100%;
  padding-top: 25px;
}

.pageWrapper {
  background-color: red;
  height:100%;
  width: 100%;
}

#gisMap {
  height: 100%;
  width: 50%;
  background-color: green;
}

source d'informationauteur sesc360