<textarea cols=50 rows=15>
哈哈。我们都是新生来得。大家都来相互帮助呀。这样我们才能进步，我们才能赚大钱！</textarea>
<input type=button value=选择字后点击我看看 onclick=alert(document.selection.createRange().text)>
</form>

function getCursortPosition(domObj) {
 var position = 0;

 if (document.selection) { //for IE
  domObj.focus();
  var sel = document.selection.createRange();
  sel.moveStart('character', -domObj.value.length);

  position = sel.text.length;
 } else if (domObj.selectionStart || domObj.selectionStart == '0') {
  position = domObj.selectionStart;
 }

 return position;
}