The following HTML represents a family tree:

<James>
  <Dave></Dave>
  <Mike></Mike>
  <Sarah></Sarah>
</James>

Implement the closestRelative function so that when a parent HTML element is passed, the function returns the parent's closest relative whose name matches the relativeName, and obeys the following rules:

The parent parameter is the HTML element of which the closest relative will be a descendant.
Each member of the family, including children, may also be a parent to one or more children.
Children are more closely related to the parent than grandchildren.
If several children in the same generation have the same name, then the first child in the tree is considered the closer relative.
If no matching relative is found the function should return null.

For example, the below code should print 'MIKE' for the given family tree:

let parent = document.getElementsByTagName('James')[0];
let relative = closestRelative(parent, 'Mike');
console.log(relative && relative.tagName); // prints MIKE