Best way to check for IE less than 9 in JavaScript without library

Javascript

var ie = (function(){

    var undef,
        v = 3,
        div = document.createElement('div'),
        all = div.getElementsByTagName('i');

    while (
        div.innerHTML = '<!--[if gt IE ' + (++v) + ']><i></i><![endif]-->',
        all[0]
    );

    return v > 4 ? v : undef;

}());

You can then do:

ie < 9

By James Panolsey from here: http://james.padolsey.com/javascript/detect-ie-in-js-using-conditional-comments

for what it's worth:

    if(  document.addEventListener  ){
        alert("you got IE9 or greater");
    }

This successfully targets IE 9+ because the addEventListener method was supported very early on for every major browser but IE. (Chrome, Firefox, Opera, and Safari) MDN Reference. It is supported currently in IE9 and we can expect it to continue to be supported here on out.

Using conditional comments, you can create a script block that will only get executed in IE less than 9.

<!--[if lt IE 9 ]>
<script>
var is_ie_lt9 = true;
</script>
<![endif]--> 

Of course, you could precede this block with a universal block that declares var is_ie_lt9=false, which this would override for IE less than 9. (In that case, you'd want to remove the var declaration, as it would be repetitive).

EDIT: Here's a version that doesn't rely on in-line script blocks (can be run from an external file), but doesn't use user agent sniffing:

Via @cowboy:

with(document.createElement("b")){id=4;while(innerHTML="<!--[if gt IE "+ ++id+"]>1<![endif]-->",innerHTML>0);var ie=id>5?+id:0}

bah to conditional comments! Conditional code all the way!!! (silly IE)

<script type="text/javascript">
/*@cc_on
   var IE_LT_9 = (@_jscript_version < 9);
@*/
</script>

Seriously though, just throwing this out there in case it suits you better... they're the same thing, this can just be in a .js file instead of inline HTML

Note: it is entirely coincidental that the jscript_version check is "9" here. Setting it to 8, 7, etc will NOT check "is IE8", you'd need to lookup the jscript versions for those browsers.