Best way to check for IE less than 9 in JavaScript

Question

What would be your fastest, shortest (best) way to detect browser which is IE and version less than 9 in JavaScript, without using jQuery or any add-on libraries?

Answer 1

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.

Answer 2

if (+(/MSIE\s(\d+)/.exec(navigator.userAgent)||0)[1] < 9) {
    // IE8 or less
}

• extract IE version with: /MSIE\s(\d+)/.exec(navigator.userAgent)
• if it's non-IE browser this will return null so in that case ||0 will switch that null to 0
• [1] will get major version of IE or undefined if it was not an IE browser
• leading + will convert it into a number, undefined will be converted to NaN
• comparing NaN with a number will always return false

Answer 3

You are all trying to overcomplicate such simple things. Just use a plain and simple JScript conditional comment. It is the fastest because it adds zero code to non-IE browsers for the detection, and it has compatibility dating back to versions of IE before HTML conditional comments were supported. In short,

var IE_version=(-1/*@cc_on,@_jscript_version@*/);

Beware of minifiers: most (if not all) will mistake the special conditional comment for a regular comment, and remove it

Basically, then above code sets the value of IE_version to the version of IE you are using, or -1 f you are not using IE. A live demonstration:

var IE_version=(-1/*@cc_on,@_jscript_version@*/);
if (IE_version!==-1){
    document.write("<h1>You are using Internet Explorer " + IE_version + "</h1>");
} else {
    document.write("<h1>You are not using a version of Internet Explorer less than 11</h1>");
}

Answer 4

If I were you I would use conditional compilation or feature detection.
Here's another alternative:

<!--[if lt IE 9]><!-->
<script>
    var LTEIE8 = true;
</script>
<!--<![endif]-->

Answer 5

Does it need to be done in JavaScript?

If not then you can use the IE-specific conditional comment syntax:

<!--[if lt IE 9]><h1>Using IE 8 or lower</h1><![endif]-->

Answer 6

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}