Pinch gestures for pdf.js

viewer.html

<script type="text/javascript">
  var gesturesSetUp = false;
  var ua = navigator.userAgent.toLowerCase();
  var isAndroid = ua.indexOf("android") > -1;

  document.addEventListener('textlayerrendered', function (e) {
    if (gesturesSetUp || e.detail.pageNumber !== PDFViewerApplication.page) {
      return;
    }

    var viewer = document.getElementById('viewer');

    // http://blog.fspm.jp/2014/06/androidpinch-inoutjsgesturestart.html

    var funcGestureStart = function (e) {};
    var funcGestureChange = function (e) {};
    var funcGestureEnd = function (e) {
      if (e.scale < 1.0) {
        // User moved fingers closer together
        document.getElementById('zoomOut').click()
      } else if (e.scale > 1.0) {
        // User moved fingers further apart
        document.getElementById('zoomIn').click()
      }
    };
     
    // iOS
    document.body.addEventListener('gesturestart', funcGestureStart, false);
    document.body.addEventListener('gesturechange', funcGestureChange, false);
    document.body.addEventListener('gestureend', funcGestureEnd, false);
     
    // Android
    if (isAndroid) {
      var pinchDistance = 0;
      var pinchScale = 1;
      document.body.addEventListener('touchstart',function(e){
        if(e.touches.length > 1){
          pinchDistance = Math.sqrt(Math.pow((e.touches[1].pageX - e.touches[0].pageX),2)+Math.pow((e.touches[1].pageY - e.touches[0].pageY),2));
          funcGestureStart(e);
        } else {
          pinchDistance = 0;
          pinchScale = 1;
        }
      },false);

      document.body.addEventListener('touchmove', function (e) {
        if (pinchDistance <= 0 || e.touches.length < 2) {
          return;
        }

        var newDistance = Math.sqrt(Math.pow((e.touches[1].pageX - e.touches[0].pageX),2)+Math.pow((e.touches[1].pageY - e.touches[0].pageY),2));
        pinchScale = newDistance / pinchDistance;
        var event = { scale: pinchScale };

        funcGestureChange(event);
      });
      document.body.addEventListener('touchend', function (e) {
        if (pinchDistance <= 0 || e.touches.length > 0) {
           return;
        }
        var event = {scale: pinchScale};
        funcGestureEnd(event);
      });
    }

    gesturesSetUp = true;
  }, true);

  document.documentElement.addEventListener('touchstart', function (event) {
    if (event.touches.length > 1) {
      event.preventDefault();
    }
  }, false);

</script>

Update: It seems the "textlayerrendered" event is not getting fired.
P.S. Even with a small pinch there is a drastic amount of zoom. Any idea why?