Determine direction currently selected text was selected (rtl vs ltr)

selectionDirection.js

var selectionIsRTL = function(sel) {
  sel = sel || document.getSelection();
  position = sel.anchorNode.compareDocumentPosition(sel.focusNode);
  return (
    // nodes are same if position === 0
    // selection direction is RTL if anchorOffset > focusOffset
    !position && sel.anchorOffset > sel.focusOffset ||
    // focus preceeds anchor
    position === Node.DOCUMENT_POSITION_PRECEDING
  )
}