判断浏览器支持的javascript版本

<script type="text/javascript">
  <!-- Begin
  var js_ver="";
  //-->
  </script>
  <script language="JavaScript1.1">
  js_ver="1.1";
  </script>
   <script language="JavaScript1.2">
  js_ver="1.2";
  </script>
   <script language="JavaScript1.3">
  js_ver="1.3";
  </script>
   <script language="JavaScript1.4">
  js_ver="1.4";
  </script>
   <script language="JavaScript1.5">
  js_ver="1.5";
  </script>
   <script language="JavaScript1.5">
  js_ver="1.6";
  </script>
   <script language="JavaScript1.7">
  js_ver="1.7";
  </script>
    <script language="JavaScript1.8">
  js_ver="1.8";
  </script>
  <script language="JavaScript1.9">
  js_ver="1.9";
  </script>
  <script type="text/javascript">
    document.write("The version of javascript is :"+js_ver);
  </script>