如何获取JS中<a>元素内部<h2>元素的id？

var aElement = document.getElementById('aId');
var h2Element = aElement.querySelector('h2');
var h2Id = h2Element.id;
console.log(h2Id);

var aElement = document.getElementById('aId');
var h2Elements = aElement.getElementsByClassName('h2Class');
for (var i = 0; i < h2Elements.length; i++) {
  var h2Id = h2Elements[i].id;
  console.log(h2Id);
}

var h2Element = document.querySelector('a#aId h2');
var h2Id = h2Element.id;
console.log(h2Id);