render hidden / invisible area with html2canvas

html2canvas-full.js

var toImg = function toImg(targetNode) {
  var tmpNode = function recreateNode(node) {
    switch (node.nodeType) {
      case 1:
	{
	  var result = document.createElement(node.nodeName);
	  var style = getComputedStyle(node);
	  for (var i = style.length - 1; i >= 0; i -= 1) {
	    result.style[style[i]] = style[style[i]];
	  }
	  switch (node.nodeName) {
	    case 'IMG':
	      {
	        result.setAttribute('src', node.getAttribute('src'));
	        break;
	      }
	    default:
	      {
	        break;
	      }
	  }
	  var child = node.firstChild;
	  while (child !== null) {
	    result.appendChild(recreateNode(child));
	    child = child.nextSibling;
	  }
	  return result;
	}
      case 3:
	{
	  return document.createTextNode(node.textContent);
	}
      default:
	{
	  break;
	}
    }
    return false;
  }(targetNode);
  var tmpNodeContainer = document.createElement('iframe');
  tmpNodeContainer.src = 'about:blank';
  document.body.append(tmpNodeContainer);
  tmpNodeContainer.contentWindow.document.body.append(tmpNode);
  tmpNode.style.overflow = 'visible';
  tmpNode.style.height = 'auto';
  tmpNodeContainer.style.transform = 'scale(0)';
  html2canvas(tmpNode).then(function (canvas) {
    document.body.removeChild(tmpNodeContainer);
    var img = document.createElement('img');
    img.src = canvas.toDataURL('image/png');
    document.body.append(img);
  });
};

其实这个只满足我当时的需求，比方说只处理了 img 的属性，别的都没管