Выбор: метод removeRange()

removeRange(range)

/* Programmatically, more than one range can be selected.
 * This will remove all ranges except the first. */
const s = window.getSelection();
if (s.rangeCount > 1) {
  for (let i = 1; i < s.rangeCount; i++) {
    s.removeRange(s.getRangeAt(i));
  }
}