Gets Last-Modified header from server and if changed reloads the style sheet.

stylereloader.js

(function(timeout, urls) {
    var times = {};
    setInterval(function() {
        for(var i = 0; i < urls.length; i++) {
            var x = new XMLHttpRequest(),
                url = urls[i];
            x.url = url;
            x.open('HEAD', url + (url.indexOf("?") === -1 ? "?v=" : "&v=") + Date.now(), true);
            x.onreadystatechange = function(e) {
                var x = e.target;
                if(x.readyState === 4 && x.status === 200) {
                    var time = new Date(x.getResponseHeader('Last-Modified'));
                    if(time.toString() !== 'Invalid Date') {
                        
                        if(times[e.target.url] === undefined || times[e.target.url].toString() !== time.toString()) {
                            document.querySelector("link[href^=\"" + e.target.url + "\"]").setAttribute("href", e.target.url);
                            times[e.target.url] = time;
                        }
                    }
                }
            }
            x.send();
        }
    }, timeout);
}(2000, ["asset/css/edetail.css", "asset/css/app.css"]));

stylereloader.min.js

!function(e,t){var a={};setInterval(function(){for(var e=0;e<t.length;e++){var r=new XMLHttpRequest,s=t[e];r.url=s,r.open("HEAD",s+(-1===s.indexOf("?")?"?v=":"&v=")+Date.now(),!0),r.onreadystatechange=function(e){var t=e.target;if(4===t.readyState&&200===t.status){var r=new Date(t.getResponseHeader("Last-Modified"));"Invalid Date"!=""+r&&(void 0===a[e.target.url]||""+a[e.target.url]!=""+r)&&(document.querySelector('link[href^="'+e.target.url+'"]').setAttribute("href",e.target.url),a[e.target.url]=r)}},r.send()}},e)}(2e3,["asset/css/edetail.css","asset/css/app.css"]);