If tested element doesn't have a parent, script fails with error

[deeppresentation]

Error:

Function where needs to be done parent null check

/**

• Tests uniqueNess of the element inside its parent
• @param { Object } element
• @param { String } Selectors
• @return { Boolean }
  */
  function testUniqueness( element, selector )
  {
  const { parentNode } = element;
  const elements = parentNode.querySelectorAll( selector );
  return elements.length === 1 && elements[ 0 ] === element;
  }