How would I best emulate the ExtJS swapStyleSheet() function using only ext-core.js?

Code:
    var origStyle = true;
    Ext.get('swapper').on('click', function(){
      if (origStyle){
        Ext.util.CSS.swapStyleSheet('ss', '/lib/css/sec.css');
      } else {
        Ext.util.CSS.swapStyleSheet('ss', '/lib/css/light.css');
      }
      origStyle = !origStyle;
    })