ReferenceError: google is not defined
<p>I want to embed google maps in to my project ,but got stuck with this issue ,i was searching for many solutions but none solved my issue. I really cant understand why this error is coming ! 
This is my javascript file</p>

<pre><code>var mapOptions = {
              zoom: 4,
              center: new google.maps.LatLng(25,80),
              mapTypeId: google.maps.MapTypeId.TERRAIN
          }

          $scope.map = new google.maps.Map(document.getElementById('map'), mapOptions);

          $scope.markers = [];

          var infoWindow = new google.maps.InfoWindow();

          var createMarker = function (info){

              var marker = new google.maps.Marker({
                  map: $scope.map,
                  position: new google.maps.LatLng(info.lat, info.long),
                  title: info.city
              });
              marker.content = '&lt;div class="infoWindowContent"&gt;' + info.desc + '&lt;/div&gt;';

              google.maps.event.addListener(marker, 'click', function(){
                  infoWindow.setContent('&lt;h2&gt;' + marker.title + '&lt;/h2&gt;' + marker.content);
                  infoWindow.open($scope.map, marker);
              });

              $scope.markers.push(marker);

          }  

          for (i = 0; i &lt; cities.length; i++){
              createMarker(cities[i]);
          }

          $scope.openInfoWindow = function(e, selectedMarker){
              e.preventDefault();
              google.maps.event.trigger(selectedMarker, 'click');
          }
</code></pre>