What is the best way to detect Internet Explorer 6 using JavaScript?

Question

What is the best way to detect Internet Explorer 6 using JavaScript?

If browser == IE6 {
    alert('hi');
}

Answer 1

Conditional comments are a good alternative:

<!--[if IE 6]>
<script>
var everythingIsBroken = true;
</script>
<![endif]-->

Edit: If you're still looking to support IE 6 in 2017 or after ... well my heart goes out to you. The answer to this question in 2017 is really not to worry about IE 6. It's not a supported browser anymore. Any operating system that can run this browser and the browser itself are not getting security updates anymore. This means users using this software are at great risk of being exploited. This is a big problem for people who can't afford to upgrade.

Answer 2

At the risk of actually answering the question that was asked (and assuming for a moment the asker has a good reason to specifically detect IE6):

if (/\bMSIE 6/.test(navigator.userAgent) && !window.opera) {
  // yep, browser claims to be IE6
}

Answer 3

  var ua = window.navigator.userAgent;
  var msie = ua.indexOf ( "MSIE " );

  if ( msie > 0 )      // If Internet Explorer, return version number
     return parseInt (ua.substring (msie+5, ua.indexOf (".", msie )));
  else                 // If another browser, return 0
     return 0;

Source : http://support.microsoft.com/kb/167820