Jak wykryć starszą przeglądarkę IE w JavaScript?

Sprawdź:

        <script type="text/javascript">
            function is_browser() {
                return (
                    navigator.userAgent.indexOf("Chrome") !== - 1 ||
                    navigator.userAgent.indexOf("Opera") !== - 1 ||
                    navigator.userAgent.indexOf("Firefox") !== - 1 ||
                    navigator.userAgent.indexOf("MSIE") !== - 1 ||
                    navigator.userAgent.indexOf("Safari") !== - 1 ||
                    navigator.userAgent.indexOf("Edge") !== - 1
                );
            }

            function less_than_ie11() {
                return (
                    !window.atob || // IE9 and below
                    Function('/*@cc_on return document.documentMode===10@*/')() // IE10
                );
            }

            function not_excluded_page() {
                return (
                    window.location.href.indexOf("/unsupported-browser/") === - 1 &&
                    document.title.toLowerCase().indexOf('page not found') === - 1
                );
            }

            if (is_browser() && less_than_ie11() && not_excluded_page()) {
                window.location = location.protocol + '//' + location.host + location.pathname + '/unsupported-browser/';
            }
        </script>