<style>
</style>
</head>
<body>
<button id = "b">open</button>
<script>
urls = [
"http://javascript.ru/forum/images/smilies/smile.gif",
"http://javascript.ru/forum/images/smilies/cray.gif"
]
flag = true
b.onclick = function(){
if(flag = !flag) return open(urls[0]); open(urls[1])
}
</script>
</body>
</html>