JSFiddle - React, Tailwind, and code Playground

HTML

<div id="Parent1">
          <div>
              <div>
                  <div id="mychildDiv"></div>
              </div>
          </div>
      </div>

CSS

div {
    height: 50px;   
    padding: 5px;    
}

div:first-child {
    float: left;
    width: auto;
    background-color: #777;
}
div:last-child {
    background-color: #77f;
    width: auto;
}

JavaScript

alert($('#mychildDiv').parents('div').last().prop('id'))