DOM tree traversal

Since at least Axel showed interest in an iterative solution, here it is:

Given two trees which have identical structure, and a specified node within the first tree, locate the node in the second tree with the same position within the structure.

If we have no other information about the two trees then the position of each node can be characterized as a path from the root node where each step in the path is specified as an index into the childNode array.

function indexOf(arrLike, target) {
    return Array.prototype.indexOf.call(arrLike, target);
}

// Given a node and a tree, extract the nodes path 
function getPath(root, target) {
    var current = target;
    var path = [];
    while(current !== root) {
        path.unshift(indexOf(current.parentNode.childNodes, current));
        current = current.parentNode;
    }
    return path;
}

// Given a tree and a path, let's locate a node
function locateNodeFromPath(root, path) {
    var current = root;
    for(var i = 0, len = path.length; i < len; i++) {
        current = current.childNodes[path[i]];
    }
    return current;
}

function getDoppleganger(rootA, rootB, target) {
    return locateNodeFromPath(rootB, getPath(rootA, target));
}

EDIT: As Blue Skies observed, childNodes doesn’t have .indexOf(). Updating with Array.prototype.indexOf.call()