JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="data" class="hidden">
  <li value="0"> 
    <ul>
      <li value="id">1</li> 
      <li value="productLine">Vintage Cars</li> 
    </ul>
  </li>
  <li value="1"> 
    <ul>
      <li value="id">2</li> 
      <li value="productLine">Ships</li>    
    </ul>
   </li>
   <li value="2"> 
    <ul>
      <li value="id">3</li> 
      <li value="productLine">Trains</li>   
    </ul>
  </li>
</ul>

JavaScript

function selectProductLine(){
    var rootUlNode = document.getElementById('data');
    var rootLiNodes = rootUlNode.children;
    var hiddenHash = {};
    for(var i=0;i< rootLiNodes.length;i++){
        var rootLiNodeValue = rootLiNodes[i].getAttribute('value');     
        var liNodes = rootLiNodes[i].firstElementChild.children;
        for(var i=0; i < liNodes.length;i++){
            hiddenHash[rootLiNodeValue] = {};
            var liNodeValue = liNodes[i].getAttribute('value');
            var liNodeContent = liNodes[i].textContent;
            hiddenHash[rootLiNodeValue][liNodeValue] = liNodeContent;
        }
    }
return hiddenHash;
}

document.write(selectProductLine());