如何找到光标的位置，以便在编辑文本时从该位置选择文本？

function getCursorPosition() {
  var cursorPos = 0;
  var sel, range;

  if (window.getSelection) {
    sel = window.getSelection();
    if (sel.rangeCount) {
      range = sel.getRangeAt(0);
      cursorPos = range.startOffset;
    }
  } else if (document.selection && document.selection.createRange) {
    range = document.selection.createRange();
    cursorPos = range.startOffset;
  }

  return cursorPos;
}