Cookie for Browser session

Any idea how one would write a cookie routine for this code to open a window only once is a browser session? The window opens when someone clicks anywhere on the page. It could become annoying if this code is on several pages. -steve-

<script>document.onclick=function () {window.open(‘http://www.mysite.com/myfolder/index.html‘, ‘nameMe’, ‘top=5,left=35,toolbar=0,menubar=0,scrollbars=1,status=0,resizable=1,width=600,height=555’);self.focus();}</script>

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