Corresponding Node Across Pages

Requirements

• Export getCorrespondingNode(rootA, rootB, target) as named and default. Return the node in rootB at the same child-index path as target under rootA.
• The roots and target are DOM Nodes. Use childNodes, so text and comment nodes count alongside elements. The roots may belong to separate documents or be detached subtrees.
• If target is rootA, return rootB. If target is outside the rootA subtree, return null. If a required child index is missing in rootB, return null.
• Normally the trees have identical child structure. Match by structural path, not node ID, text, class name, or tag name. Do not reject a valid path just because content or tags differ.
• Return the existing destination node by identity. Do not clone, mutate either tree, or modify target. If both roots are the same, a descendant maps to itself.
• DOM changes during the call, shadow roots, slots, and cross-origin frame access are outside scope. The function receives accessible node references rather than loading another page.

Examples

Input: // Tree A: <div><p>First</p><button>Save</button></div>
// Tree B: <div><p>Second</p><button>Submit</button></div>
getCorrespondingNode(rootA, rootB, rootA.childNodes[1]);
Output: Returns the existing button node from tree B.

Input: getCorrespondingNode(rootA, rootB, rootA);
Output: Returns rootB itself.