<input type="radio" name="a" value="张三" id="a1" />
       <input type="radio" name="a" value="曾四" id="a2"/>
  显示被选中的Radio  
       l=document.getElementsByName("a");
       
       for(i=0 ; i< l.length ; i++)
       {
         alert(l[i].value);
       }