HTMLTextAreaElement: selectionDirection property

The selectionDirection property of the HTMLTextAreaElement interface specifies the current direction of the selection. The possible values are "forward", "backward", and "none". The forward value indicates the selection was performed in the start-to-end direction of the current locale, with backward indicating the opposite direction. The none value occurs if the direction is unknown. It can be used to both retrieve and change the direction of the <textarea>s selected text.

Setting the selectionDirection to a new value fires the selectchange and select events.

const textarea = document.getElementById("text-box");
const end = textarea.selectionDirection;