function getSelection(node) {
  if ('selectionStart' in node &&
      ReactInputSelection.hasSelectionCapabilities(node)) {
    return {
      start: node.selectionStart,
      end: node.selectionEnd
    };
  } else if (window.getSelection) {
    var selection = window.getSelection();
    return {
      anchorNode: selection.anchorNode,
      anchorOffset: selection.anchorOffset,
      focusNode: selection.focusNode,
      focusOffset: selection.focusOffset
    };
  } else if (document.selection) {
    var range = document.selection.createRange();
    return {
      parentElement: range.parentElement(),
      text: range.text,
      top: range.boundingTop,
      left: range.boundingLeft
    };
  }
}
Get an object which is a unique representation of the current selection.

The return value will not be consistent across nodes or browsers, but
two identical selections on the same node will return identical objects.

@param {DOMElement} node
@param {object}