JS 中replaceAll的用法

<script language="javascript">
  String.prototype.replaceAll  = function(s1,s2){   
    return this.replace(new RegExp(s1,"g"),s2);   
  }
   function test() {
    var sl = 'abcd&efg&gg&';
    sl = sl.replaceAll("&","&amp;");
    alert(sl);
   }
  </script>