The following script allows you to extract the username of the current Windows user within an HTML page using Javascript.

<script>

var wshshell=new ActiveXObject("wscript.shell");

var username=wshshell.ExpandEnvironmentStrings("%username%");

alert(username);

</script>

It only works within Internet Explorer so is probably only of any use within controlled environments where the browser is of a a known flavour.

The script may trigger a security warning which the user will have to accept before the username is available.