ionic2 TypeScript shows error: Cannot find name 'google' and '$', but google map and jquery still works
<p>I am trying to build a ionic2 application using TypeScript.</p>

<p>In index.html, I've tried to plug the jquery and google map JS API into it before cordova.js:</p>

<pre><code>  &lt;!-- Vendor --&gt;
  &lt;script src="https://maps.googleapis.com/maps/api/js?key=XXXXX&amp;signed_in=false"&gt;&lt;/script&gt;
  &lt;script src="asset/jquery.min.js"&gt;&lt;/script&gt;

  &lt;!-- cordova.js required for cordova apps --&gt;
  &lt;script src="cordova.js"&gt;&lt;/script&gt;
</code></pre>

<p>The google map and jquery inside the app is working normally, however just wondering why these error messages shows when I run "ionic serve" command</p>

<pre><code>TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(15,21): Error TS2304: Cannot find name 'google'.
TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(30,18): Error TS2304: Cannot find name 'google'.
TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(37,24): Error TS2304: Cannot find name 'google'.
TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(39,5): Error TS2304: Cannot find name '$'.
TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(39,42): Error TS2304: Cannot find name '$'.
TypeScript error: /Users/xxx/client_app/app/pages/step1/step1.ts(39,76): Error TS2304: Cannot find name '$'.
</code></pre>

<p>Here are part of my code in step1.ts:</p>

<pre><code>  ngOnInit() {
    this.gmap = new google.maps.Map(document.getElementById('gmap_canvas'), {
            center: {
                lat: 22.280102,
                lng: 114.183751
            },
            zoom: 16,
            streetViewControl: false,
            styles : [{
                featureType: "poi",
                elementType: "labels",
                stylers: [
                    { visibility: "off" }
                ]
            }],
            mapTypeControlOptions: {
                mapTypeIds: [google.maps.MapTypeId.ROADMAP]
            },
            overviewMapControl: false,
            mapTypeControl: false,
        });

    this.gmap.controls[google.maps.ControlPosition.TOP_CENTER].push(document.getElementById('gmep_center_marker'));

    $('#gmep_center_marker').css({ top: ($('#gmap_canvas').height() / 2) - $('#gmep_center_marker').height() });
  }
</code></pre>