The labels read-only property of the ElementInternals interface returns the labels associated with the element.

A NodeList containing all of the label elements associated with this element.

The following example shows a custom checkbox component with a <label> element linked to it. Printing the value of labels to the console returns a NodeList with one entry, representing this label.

<form id="myForm">
  <custom-checkbox id="custom-checkbox"></custom-checkbox>
  <label for="custom-checkbox">Join newsletter</label>
</form>

let element = document.getElementById("custom-checkbox");
console.log(element.internals_.label);