How can you get the JS version of a visitor's browser?

I can do it like this but I do not want to use this method:

Code:
<SCRIPT language="javascript">

var js="1.0";

</SCRIPT>


<SCRIPT language="javascript1.1">

js="1.1";

</SCRIPT>


<SCRIPT language="javascript1.2">

js="1.2";

</SCRIPT>


<SCRIPT language="javascript1.3">

js="1.3";

</SCRIPT>


<SCRIPT language="javascript1.4">

js="1.4";

</SCRIPT>


<script language="javascript">

document.write(js);

</script>
Any suggestions?

Sean