IE.js

var IE = (function() { 
        if (document.documentMode) {
            return document.documentMode;
        } else {
            for (var i = 7; i > 4; i--) {
                var div = document.createElement("div");

                div.innerHTML = "<!--[if IE " + i + "]><span></span><![endif]-->";

                if (div.getElementsByTagName("span").length) {
                    div = null;

                    return i;
                }
            }
        }

        return undefined;
    })();