Previous Left Sibling

Question

Given a DOM tree and a target element, please return the previous left sibling.

Like above, the previous left sibling of green <a/> is the blue <button/>. Notice that they don't necessarily have the same parent element.

If no left sibling, then return null.

What is time & space cost of your solution ?

Code

/**
 * @param {Element} root
 * @param {Element} target
 * @return {Elemnt | null}
 */
function previousLeftSibling(root, target) {
  // your code here
}

Source

Source From