SOURCE

/* 
作者：TangPoems
链接：https://www.nowcoder.com/discuss/871077?type=post&order=create&pos=&page=1&ncTraceId=&channel=-1&source_id=search_post_nctrack&subType=2&gio_id=4B11D26016AC8D56CAC57B6E316F3069-1648730048097
来源：牛客网

{
 tag:'DIV',
 children:[
     {tag:'SPAN'
      children:[{tag:'DIV',
            children:[]},
 
            {tag:'DIV',
             children:[]}
                    ]},
 
      {tag:'SPAN'
      children:[{tag:'DIV',
            children:[]},
 
           {tag:'DIV',
            children:[]}
           ]}
     ]
}

*/

function getTree (root) {
    const obj = Object.create(null)
    obj.tag = root && (root.tagName || '')
    obj.children = []
    for (let i = 0; i < root.children.length; i++) {
        obj.children.push(getTree(root.children[i]))
    }
    return obj
}

console.log(getTree(document.querySelectorAll('div')[0]))

<div>
  <span>
     <div></div>
     <div></div>
  </span>
  <span>
      <div></div>
      <div></div>
  </span>
</div>