window.onload = function () {
      // 阻止双击放大
      var lastTouchEnd = 0;
      document.addEventListener('touchstart', function (event) {
        if (event.touches.length > 1) {
          event.preventDefault();
        }
      });
      document.addEventListener('touchend', function (event) {
        var now = (new Date()).getTime();
        if (now - lastTouchEnd <= 300) {
          event.preventDefault();
        }
        lastTouchEnd = now;
      }, false);

      // 阻止双指放大
      document.addEventListener('gesturestart', function (event) {
        event.preventDefault();
      });
    };