如何判断自己的浏览器支持的是javascript的那个版本

  <script language="javascript">
         var jsversion = 1.0;
 </script>
 <script language="javascript1.1">
 jsversion = 1.1;
 </script>
 <script language="javascript1.2">
 jsversion = 1.2;
 </script>
 <script language="javascript1.3">
 jsversion = 1.3;
 </script>
 <script language="javascript1.4">
 jsversion = 1.4;
 </script>
 <script language="javascript1.5">
 jsversion = 1.5;
 </script>
 <script language="javascript1.6">
 jsversion = 1.6;
 </script>
 <script language="javascript1.7">
 jsversion = 1.7;
 </script>
 <script language="javascript1.8">
 jsversion = 1.8;
 </script>
 <script language="javascript1.9">
 jsversion = 1.9;
 </script>
 <script language="javascript2.0">
 jsversion = 2.0;
 </script>
 <script language="javascript">
     document.write('你的浏览器支持 JavaScript ' + jsversion)
 </script>