拖动iframe时，iOS上的iframe会移位

iframe {
  touch-action: none;
}

var iframe = document.getElementById('my-iframe');
var startX, startY;

iframe.addEventListener('touchstart', function(e) {
  startX = e.touches[0].clientX - iframe.offsetLeft;
  startY = e.touches[0].clientY - iframe.offsetTop;
});

iframe.addEventListener('touchmove', function(e) {
  e.preventDefault();
  var offsetX = e.touches[0].clientX - startX;
  var offsetY = e.touches[0].clientY - startY;
  iframe.style.left = offsetX + 'px';
  iframe.style.top = offsetY + 'px';
});