有没有办法在IE的输入框中获取所选文本的偏移量？

function getSelectionOffset() {
  var selection = document.selection;
  var range = selection.createRange();
  var textRange = document.body.createTextRange();
  textRange.moveToElementText(range.parentElement());
  for (var i = 0; i< range.text.length; i++) {
    if (range.text.charAt(i) == range.text) {
      break;
    }
    textRange.moveStart('character', 1);
  }
  return textRange.offset;
}