Stylesheet Switcher

switcher.js

(function() {
  const links = Array.from( document.querySelectorAll( 'link[title]' ) );
  const styles = Array.from( new Set( links.map( link => link.title ) ) );
  let title = localStorage.getItem( 'title' );

  function selectStyle( title ) {
    links.forEach( link => {
      link.disabled = true;
      link.disabled = link.title !== title;
    });

    localStorage.setItem( 'title', title );
  }

  if ( styles.length > 1 ) {
    const select = document.createElement( 'select' );

    if ( title ) {
      selectStyle( title );
    }
    select.setAttribute( 'style', 'position: absolute; top: 1em; right: 1em;' );
    for ( let i = 0; i < styles.length; i++ ) {
      const option = document.createElement( 'option' );
      option.text = 'CSS: ' + styles[ i ];
      option.value = styles[ i ];
      option.selected = styles[ i ] === title;
      select.add( option );
    }
    document.body.appendChild( select );

    select.addEventListener( 'change', function( event ) {
      title = event.target.options[ event.target.selectedIndex ].value; 
      selectStyle( title );
    });
  }
}());