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Find Identical Node in DOM Tree

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>DOM Traversal</title>
  </head>
  <body>
    <div id="rootA">
      <div>
        <div></div>
      </div>
      <div></div>
      <div>
        <div>
          <div id="nodeA"></div>
          <div></div>
        </div>
      </div>
    </div>

    <div id="rootB">
      <div>
        <div></div>
      </div>
      <div></div>
      <div>
        <div>
          <div id="nodeB">Node B</div>
          <div></div>
        </div>
      </div>
    </div>
  </body>
</html>

const rootA = document.getElementById("rootA");
const rootB = document.getElementById("rootB");
const nodeA = document.getElementById("nodeA");

const path = [];
const findPath = () => {
  let currNode = nodeA;
  while (currNode !== rootA) {
    path.push(
      [...currNode.parentElement.children]
      .indexOf(currNode)
    );
    currNode = currNode.parentElement;
  }
};

const findB = () => {
  let currNode = rootB;
  while (path.length) {
    currNode = currNode.children[path.pop()];
  }
  return currNode;
};

findPath();

console.log(findB().innerHTML); // Node B

Demo