Outdated Browser - minified to return just boolean

outdatedBrowser.js

/**
 * Outdated Browser
 * Version:    1.1.2 - 2015
 * author:     Burocratik
 * website:    http://www.burocratik.com
 */
var isOutdatedBrowser = function(lowerThan) {

    //assign css3 property or js property to IE browser version
    if (lowerThan == 'IE8' || lowerThan == 'borderSpacing') {
        lowerThan = 'borderSpacing';
    } else if (lowerThan == 'IE9' || lowerThan == 'boxShadow') {
        lowerThan = 'boxShadow';
    } else if (lowerThan == 'IE10' || lowerThan == 'transform' || lowerThan == '' || typeof lowerThan === "undefined") {
        lowerThan = 'transform';
    } else if (lowerThan == 'IE11' || lowerThan == 'borderImage') {
        lowerThan = 'borderImage';
    }  else if (lowerThan == 'Edge' || lowerThan == 'js:Promise') {
        lowerThan = 'js:Promise';
    }

    if (!lowerThan) {
        lowerThan = 'transform';
    }

    cssProp = lowerThan;

    var supports = ( function() {
        var div = document.createElement('div');
        var vendors = 'Khtml Ms O Moz Webkit'.split(' ');
        var len = vendors.length;

        return function(prop) {
            if (prop in div.style) return true;

            prop = prop.replace(/^[a-z]/, function(val) {
                return val.toUpperCase();
            });

            while (len--) {
                if (vendors[len] + prop in div.style) {
                    return true;
                }
            }
            return false;
        };
    } )();

    var validBrowser = false;

    // browser check by js props
    if(/^js:+/g.test(cssProp)) {
        var jsProp = cssProp.split(':')[1];
        if(!jsProp)
            return;

        switch (jsProp) {
            case 'Promise':
                validBrowser = window.Promise !== undefined && window.Promise !== null && Object.prototype.toString.call(window.Promise.resolve()) === '[object Promise]';
                break;
            default:
                validBrowser = false;
        }
    } else {
        // check by css3 property (transform=default)
        validBrowser = supports('' + cssProp + '');
    }

    return !validBrowser;
};