code: function scaleImage(evt) {
          var moveTouces = getTouches(evt.targetTouches);
          var scale = calculateScale(startTouches, moveTouces);
          var node = zoomNode;
          scale = currentScale * scale < minScale ? minScale : currentScale * scale;
          node.style.webkitTransform = generateTranslate(0, 0, 0, scale);
      }
docs: scale image
  @param {object} evt