JavaScript Call Random CSS file

Someone talk to stack overflow like this :

I am trying to rotate random CSS sheets via JS - I have the following script but when I am using it - it doesnt seem to work ?

function getRand(){
    return Math.round(Math.random()*(css.length-1));
}
var css = new Array(
'<link rel="stylesheet" type="text/css" href="css/1.css">',
'<link rel="stylesheet" type="text/css" href="css/2.css">',
'<link rel="stylesheet" type="text/css" href="css/3.css">',
'<link rel="stylesheet" type="text/css" href="css/4.css">'
);
rand = getRand();
document.write(css[rand]);

Appreciate any help?

The best answer is : Try to create the link element programmatically and appending it to the head

function applyRandCSS(){
  var css = ["css/1.css", "css/2.css", "css/3.css", "css/4.css"];
  var randomFile = css[Math.round(Math.random()*(css.length-1))];
  var ss = document.createElement("link");

  ss.type = "text/css";
  ss.rel = "stylesheet";
  ss.href = randomFile;

  document.getElementsByTagName("head")[0].appendChild(ss);
}

Source : https://stackoverflow.com/questions/1244877/random-css-via-js