How to check browser version?

<script>

    function myFunction() { 
     if((navigator.userAgent.indexOf("Opera") || navigator.userAgent.indexOf('OPR')) != -1 ) 
    {
        alert('Opera');
    }
    else if(navigator.userAgent.indexOf("Chrome") != -1 )
    {
        alert('Chrome');
    } else{
 
 }
</script>

<SCRIPT LANGUAGE="JavaScript">
var browsername;
var browserVersion;
function checkBrowser() {
  browsername = navigator.appName;
  // Sets the version number (e.g., 4.03)
  browserVersion = parseFloat(navigator.appVersion);
  if(browsername.indexOf("Netscape")!= -1) {
    browsername="NS";
  } else {
    if(browsername.indexOf("Microsoft")!=-1) {
      browsername="MSIE";
    } else {
      browsername="N/A";
      alert("Unknown browser: " + browsername);
    }
  }
  //-- code goes here........
  alert("Your Browser Name : " + browsername + " Version : " + browserVersion);
}
</SCRIPT>

Call the above functions on the body onload event.