Trim function in javascript

The javascript code below will trim the leading and trailing spaces from a string.

<script language="javascript">

function trim(str)
{
 while(''+str.charAt(0)==' ')
  str=str.substring(1,str.length);
  while(''+str.charAt(str.length-1)==' ')
   str=str.substring(0,str.length-1);
 return str;
}

</script>