return node.tagName.toLowerCase() == 'p' ?

    NodeFilter.FILTER_ACCEPT:

    NodeFilter.FILTER_REJECT;

}

var iterator = document.createNodeIterator(root, NodeFilter.SHOW_ELEMENT, filter, false);

var node = iterator.nextNode();

while(node !== null){

    console.log( node.tagName ); 

    // node 的属性 与方法 详见 2 nodeFilter

    node = iterator.nextNode();

}

 ————————————————

基于此，可以简单的做为 web node 节点的数据 采集

var nodeIterator = document.createNodeIterator(

  // Node to use as root

  document.getElementById('someId'),

  // Only consider nodes that are text nodes (nodeType 3)

  NodeFilter.SHOW_TEXT,

  // Object containing the function to use for the acceptNode method

  // of the NodeFilter

    { acceptNode: function(node) {

      // Logic to determine whether to accept, reject or skip node

      // In this case, only accept nodes that have content

      // other than whitespace

      if ( ! /^\s*$/.test(node.data) ) {

        return NodeFilter.FILTER_ACCEPT;

      }

    }

  },

  false

);

// Show the content of every non-empty text node that is a child of root

var node;

while ((node = nodeIterator.nextNode())) {

  alert(node.data);

}

while(node !== null){

    console.log( node.tagName );

   //node.tagName  等于 element.tagName

  // element 的属性 与方法 详见 3、

    node = iterator.nextNode();

}