How to add username to my button link

How to add username to my button link

Hi,
My button name is et_pb_promo_button and i want that when some one clicks on that then link open in new tab and add key=username ..but there is something wrong iin my code.
it opens in new tab but doesn't add username
<script type="text/javascript">
jQuery(document).ready(function(){
jQuery(".et_pb_promo_button").attr("target","_blank").attr("target","username");});
</script>