Click on this link to see which version your BROWSER is using: http://jsfiddle.net/Ac6CT/
You should be able filter by using script tags to each JS version.
<script type="text/javascript">
var jsver = 1.0;
</script>
<script language="Javascript1.1">
jsver = 1.1;
</script>
<script language="Javascript1.2">
jsver = 1.2;
</script>
<script language="Javascript1.3">
jsver = 1.3;
</script>
<script language="Javascript1.4">
jsver = 1.4;
</script>
<script language="Javascript1.5">
jsver = 1.5;
</script>
<script language="Javascript1.6">
jsver = 1.6;
</script>
<script language="Javascript1.7">
jsver = 1.7;
</script>
<script language="Javascript1.8">
jsver = 1.8;
</script>
<script language="Javascript1.9">
jsver = 1.9;
</script>
<script type="text/javascript">
alert(jsver);
</script>
My Chrome reports 1.7
Blatantly stolen from: http://javascript.about.com/library/bljver.htm
<script>
function (JSVer());
// STEP ONE: Convert all characters to lowercase to simplify testing
var agt=navigator.userAgent.toLowerCase();
// SETP TWO: Determine Browser Version
// Note: On IE5, these return 4, so use is_ie5up to detect IE5.
var is_major = parseInt(navigator.appVersion);
var is_minor = parseFloat(navigator.appVersion);
// Note: Opera and WebTV spoof Navigator. We do strict client detection.
// If you want to allow spoofing, take out the tests for opera and webtv.
var is_nav = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
&& (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
&& (agt.indexOf('webtv')==-1) && (agt.indexOf('hotjava')==-1));
var is_nav2 = (is_nav && (is_major == 2));
var is_nav3 = (is_nav && (is_major == 3));
var is_nav4 = (is_nav && (is_major == 4));
var is_nav4up = (is_nav && (is_major >= 4));
var is_navonly = (is_nav && ((agt.indexOf(";nav") != -1) ||
(agt.indexOf("; nav") != -1)) );
var is_nav6 = (is_nav && (is_major == 5));
var is_nav6up = (is_nav && (is_major >= 5));
var is_gecko = (agt.indexOf('gecko') != -1);
var is_ie = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));
var is_ie3 = (is_ie && (is_major < 4));
var is_ie4 = (is_ie && (is_major == 4) && (agt.indexOf("msie 4")!=-1) );
var is_ie4up = (is_ie && (is_major >= 4));
var is_ie5 = (is_ie && (is_major == 4) && (agt.indexOf("msie 5.0")!=-1) );
var is_ie5_5 = (is_ie && (is_major == 4) && (agt.indexOf("msie 5.5") !=-1));
var is_ie5up = (is_ie && !is_ie3 && !is_ie4);
var is_ie5_5up =(is_ie && !is_ie3 && !is_ie4 && !is_ie5);
var is_ie6 = (is_ie && (is_major == 4) && (agt.indexOf("msie 6.")!=-1) );
var is_ie6up = (is_ie && !is_ie3 && !is_ie4 && !is_ie5 && !is_ie5_5);
// KNOWN BUG: On AOL4, returns false if IE3 is embedded browser
// or if this is the first browser window opened. Thus the
// variables is_aol, is_aol3, and is_aol4 aren't 100% reliable.
var is_aol = (agt.indexOf("aol") != -1);
var is_aol3 = (is_aol && is_ie3);
var is_aol4 = (is_aol && is_ie4);
var is_aol5 = (agt.indexOf("aol 5") != -1);
var is_aol6 = (agt.indexOf("aol 6") != -1);
var is_opera = (agt.indexOf("opera") != -1);
var is_opera2 = (agt.indexOf("opera 2") != -1 || agt.indexOf("opera/2") != -1);
var is_opera3 = (agt.indexOf("opera 3") != -1 || agt.indexOf("opera/3") != -1);
var is_opera4 = (agt.indexOf("opera 4") != -1 || agt.indexOf("opera/4") != -1);
var is_opera5 = (agt.indexOf("opera 5") != -1 || agt.indexOf("opera/5") != -1);
var is_opera5up = (is_opera && !is_opera2 && !is_opera3 && !is_opera4);
var is_webtv = (agt.indexOf("webtv") != -1);
var is_TVNavigator = ((agt.indexOf("navio") != -1) || (agt.indexOf("navio_aoltv") != -1));
var is_AOLTV = is_TVNavigator;
var is_hotjava = (agt.indexOf("hotjava") != -1);
var is_hotjava3 = (is_hotjava && (is_major == 3));
var is_hotjava3up = (is_hotjava && (is_major >= 3));
// STEP THREE: Associate Javascript Version with Browser
var is_js;
if (is_nav2 || is_ie3) is_js = 1.0;
else if (is_nav3) is_js = 1.1;
else if (is_opera5up) is_js = 1.3;
else if (is_opera) is_js = 1.1;
else if ((is_nav4 && (is_minor <= 4.05)) || is_ie4) is_js = 1.2;
else if ((is_nav4 && (is_minor > 4.05)) || is_ie5) is_js = 1.3;
else if (is_hotjava3up) is_js = 1.4;
else if (is_nav6 || is_gecko) is_js = 1.5;
// NOTE: In the future, update this code when newer versions of JS
// are released. For now, we try to provide some upward compatibility
// so that future versions of Nav and IE will show they are at
// *least* JS 1.x capable. Always check for JS version compatibility
// with > or >=.
else if (is_nav6up) is_js = 1.5;
// NOTE: ie5up on mac is 1.4
else if (is_ie5up) is_js = 1.3
// HACK: no idea for other browsers; always check for JS version with > or >=
else is_js = 0.0;
return (is_js) ;
</script>