unique-selector/src/isUnique.js

Given a DOM node, return a unique CSS selector matching only that element

/**
 * Checks if the selector is unique
 * @param  { Object } element
 * @param  { String } selector
 * @return { Array }
 */
export function isUnique( el, selector )
{
  if( !Boolean( selector ) ) return false;
  const elems = el.ownerDocument.querySelectorAll( selector );
  return elems.length === 1 && elems[ 0 ] === el;
}