The ariaOrientation property of the Element interface reflects the value of the aria-orientation attribute, which indicates whether the element's orientation is horizontal, vertical, or unknown/ambiguous.

A string with one of the following values:

"horizontal"

The element is horizontal.

"vertical"

The element is vertical.

"undefined"

The element's orientation is unknown.

In this example the aria-orientation attribute on the element with an ID of handle_zoomSlider is set to "vertical". Using ariaOrientation we update the value to "horizontal".

<div
  id="handle_zoomSlider"
  role="slider"
  aria-orientation="vertical"
  aria-valuemin="0"
  aria-valuemax="17"
  aria-valuenow="14"
  tabindex="0">
  <span>11</span>
</div>

let el = document.getElementById("handle_zoomSlider");
console.log(el.ariaOrientation); // "vertical"
el.ariaOrientation = "horizontal";
console.log(el.ariaOrientation); // "horizontal"