정규식으로 바꿨습니다.

많이 돌아 다니는 소스이긴 하지만..

 

<SCRIPT LANGUAGE="JavaScript">
<!--
 String.prototype.trim = function() {return this.replace(/(^\s*)|(\s*$)/g, "");}
 String.prototype.ltrim = function() {return this.replace(/(^\s*)/g, "");}
 String.prototype.rtrim = function() {return this.replace(/(\s*$)/g, "");}

 

 function res(){
  if(document.form.sel.value == "1")
   document.form.rep.value = document.form.ok.value.trim();
  if(document.form.sel.value == "2")
   document.form.rep.value = document.form.ok.value.rtrim();
  if(document.form.sel.value == "3")
   document.form.rep.value = document.form.ok.value.ltrim();
 }
//-->
</SCRIPT>
</HEAD>

<BODY>

<form name="form">
  <select name="sel">
    <option value="1">Trim</option>
    <option value="2">rTrim</option>
    <option value="3">lTrim</option>
  </select>
  <input type="text" name="ok" >
  <input type="text" name="rep" >
  <input type="button" value="확인" onclick="res();"><br>

</form>
</BODY>