title: Check active style sheet from js code (check cookie for active style sheet)
body: <p>I have a code for writing/reading cookie for active style sheet (CSS switcher):</p>
  
  <pre><code>function setActiveStyleSheet(title) {
    var i, a, main;
    for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
      if(a.getAttribute("rel").indexOf("style") != -1 &amp;&amp; a.getAttribute("title")) {
        a.disabled = true;
        if(a.getAttribute("title") == title) a.disabled = false;
      }
    }
  }
  
  function getActiveStyleSheet() {
    var i, a;
    for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
      if(a.getAttribute("rel").indexOf("style") != -1 &amp;&amp; a.getAttribute("title") &amp;&amp; !a.disabled) return a.getAttribute("title");
    }
    return null;
  }
  
  function getPreferredStyleSheet() {
    var i, a;
    for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
      if(a.getAttribute("rel").indexOf("style") != -1
         &amp;&amp; a.getAttribute("rel").indexOf("alt") == -1
         &amp;&amp; a.getAttribute("title")
         ) return a.getAttribute("title");
    }
    return null;
  }
  
  function createCookie(name,value,days) {
    if (days) {
      var date = new Date();
      date.setTime(date.getTime()+(days*24*60*60*1000));
      var expires = "; expires="+date.toGMTString();
    }
    else expires = "";
    document.cookie = name+"="+value+expires+"; path=/";
  }
  
  function readCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for(var i=0;i &lt; ca.length;i++) {
      var c = ca[i];
      while (c.charAt(0)==' ') c = c.substring(1,c.length);
      if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
    }
    return null;
  }
  
  window.onload = function(e) {
    var cookie = readCookie("style");
    var title = cookie ? cookie : getPreferredStyleSheet();
    setActiveStyleSheet(title);
  }
  
  window.onunload = function(e) {
    var title = getActiveStyleSheet();
    createCookie("style", title, 365);
  }
  
  var cookie = readCookie("style");
  var title = cookie ? cookie : getPreferredStyleSheet();
  setActiveStyleSheet(title);
  </code></pre>
  
  <p>and two lines in html:</p>
  
  <pre><code>   &lt;link rel="stylesheet" href="main.css"&gt;
     &lt;link rel="alternate stylesheet" href="darkmode.css" title="darkmode"&gt;
     &lt;script src="styleswitcher.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>I want to set checkbox to “checked” if darkmode.css is active.</p>
  
  <p>The question is:
  <strong>How I can check if darkmode.css is active in single line JavaScript code from external .js file according listed code?</strong></p>