function Element(option) {
  this.id = option.id || '';
  this.nodeName = option.nodeName || '';
  this.nodeValue = option.nodeValue || '';
  this.nodeType = 1;
  this.children = option.children || [];
}
var doc = new Element({
  nodeName: 'html'
});
var head = new Element({
  nodeName: 'head'
});
var body = new Element({
  nodeName: 'body'
})
doc.children.push(head);
doc.children.push(body);
var div = new Element({
  nodeName: 'div',
  nodeValue: 'haha',
});
var p = new Element({
  nodeName: 'p',
  nodeValue: '段落'
})
body.children.push(div);
body.children.push(p);
function getChildren(ele) {
  for(var i = 0; i < ele.children.length; i++) {
    var child = ele.children[i];
    console.log(child.nodeName);
    getChildren(child);
  }
}
getChildren(doc);