The core difference between the lastChild and lastElementChild DOM element properties is that,

• The lastChild DOM element property returns a text, comment, or an Element that comes as the last in a parent element. Put simply, it returns the last thing whether it may be of text, comment, or an Element type.

• The lastElementChild element property, on the other hand, returns the last Element type as the value. Even If there are text or comment which comes after it, it doesn't return the text or the comment as the values.

Let's look at an example.

Consider this div tag with:

• span tag
• text of Hello World!
• a paragraph tag
• another text of Hai, I'm another simple text

inside it as its children.

<div>
  <span>I'm inside a SPAN tag</span>
  Hello World!
  <p>I'm a paragraph</p>
  Hai, I'm another simple text.
</div>

Now let's use the lastChild and the lastElementChild DOM element properties on the div element to check what it returns.

// get reference to the div tag
const div = document.querySelector("div");

// lastChild DOM element property
const lastChild = div.lastChild;

// lastElementChild DOM element property
const lastElementChild = div.lastElementChild;

console.log(lastChild); // Hai, I'm another simple text.

console.log(lastElementChild); // <p>I'm a paragraph</p>

As you can see the lastChild returns the last text content Hai, I'm another simple text and the lastElementChild returns the last element i.e para tag (<p>I'm a paragraph</p>).

See this example live in JSBin.

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