关于在浏览器里面保存目标文件是.txt文件类型的问题？急！！！！

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD><BODY>
<img src="2.BMP" onclick="mm(this)"><SCRIPT LANGUAGE="JavaScript">
function mm(e) //&Otilde;&acirc;&cedil;&ouml;·&frac12;·¨&Ouml;&raquo;&Otilde;&euml;&para;&Ocirc;&Iacute;&frac14;&AElig;&not;
{
  var w = window.open(e.src, "_blank", "width=100,height=100");
  w.document.execCommand('Saveas');
  w.close()
}
</SCRIPT>
<a href="#" onclick="download();">&Icirc;&Auml;&frac14;&thorn;&Ograve;&raquo;&Iuml;&Acirc;&Ocirc;&Oslash;</a><script language="JavaScript">
<!--
function download(){
var win=window.open("&sup2;&Ugrave;×÷&sup2;&frac12;&Ouml;è.txt");
win.document.execCommand("saveas");
win.close();
}
//-->
</script></BODY>
</HTML>