JavaScript 创建新的CSS选择器（FF，IE，Opera）

Posted 2021-05-20

//see Flanagan 5th ed. 16.6
    var menuId = 'foo';
    var selector = '#'+ menuId + ' li ul';
    //assume we have at least one stylesheet
    if ( document.styleSheets[0].insertRule) {
      //if not IE
       var lastrule = document.styleSheets[0].cssRules.length;
      document.styleSheets[0].insertRule(selector + '{display:none}', lastrule);  
    } else if ( document.styleSheets[0].addRule ) {
      //if IE
      var lastrule = document.styleSheets[0].rules.length;
      document.styleSheets[0].addRule(selector, 'display:none', lastrule);
    }