loadCSS.js

/*!
loadCSS: load a CSS file asynchronously.
[c]2014 @scottjehl, Filament Group, Inc.
Licensed MIT
*/
function loadCSS( href, before, media ){
  "use strict";
  // Arguments explained:
  // `href` is the URL for your CSS file.
  // `before` optionally defines the element we'll use as a reference for injecting our <link>
  // By default, `before` uses the first <script> element in the page.
  // However, since the order in which stylesheets are referenced matters, you might need a more specific location in your document.
  // If so, pass a different reference element to the `before` argument and it'll insert before that instead
  // note: `insertBefore` is used instead of `appendChild`, for safety re: http://www.paulirish.com/2011/surefire-dom-element-insertion/

  // DELETE OLD STYLESHEET IF IT ALREADY EXISTS
  var current_ss = window.document.getElementsByTagName( "link" );
  // loop through each stylesheet in the DOM as `ss`
  for ( var i = 0, ss; ss = current_ss[i]; i++ ) {
    console.log(ss);
    // <link rel="stylesheet" href="test.css" media="all">
    console.log(ss.media);
    // "only x"
    if ( ss.href === href && ss.media === media ) {
      ss.remove();
    }
  }

  // ADD THE NEW STYLESHEET
  var ss = window.document.createElement( "link" );
  var ref = before || window.document.getElementsByTagName( "script" )[ 0 ];
  ss.rel = "stylesheet";
  ss.href = href;
  // temporarily, set media to something non-matching to ensure it'll fetch without blocking render
  ss.media = "only x";
  // inject link
  ref.parentNode.insertBefore( ss, ref );
  // set media back to `all` so that the styleshet applies once it loads
  setTimeout( function(){
    ss.media = media || "all";
  } );
}

loadCSS("test.css");