Edit in JSFiddle

        //var version1 = document.all ? /(\d){1}/g.exec(window.navigator.userAgent.split(';')[1].replace(/^(\s){1,}|(\s){1,}$/g, ''))[1] : undefined;

        // 첫 번째 방법
        var version1 = document.all ? /(\d){1}/g.exec(window.navigator.userAgent.split(';')[1])[1] : undefined;

        alert(version1); // my ie version


        // 두 번째 방법
        var version2 = (function () {

            if (!document.all) return undefined;

            var v = 4
              , div = document.createElement('div')
              , f = div.getElementsByTagName('i');

            while (!f[0]) {
                div.innerHTML = '<!--[if IE ' + (v) + ']><i></i><![end if]-->';
                v++;
            }
            
            v = v - 1;

            return v >= 4 ? v : undefined;

        })();
        
        alert(version2); // my ie version
        
        // javascript 연산자 테스트            
        var num = 1;
        while (num = 0, num);

        alert(num); // 0