<html>
<head>
<title>URL</title>

<script>
function go() {

if ((document.form.url.value==""))
{alert("URL을 입력하여 주세요");
return false;
}
window.open(""+document.form.url.value+"")
}
</script>
</head>

<body>

<form name="form" method="post" onsubmit="return go();">

주소를 입력하여 주세요: <input type="text" value="" name="url">

<input type="button" value="Go.." onclick="go()">
<input type="reset" value="초기화">
</form>

</body>
</html>