modalindex.html

<html>
<head>
<title>Main window</title>
<script>
  function openModal() {
    window.showModalDialog("modal_1.html",'dialogWidth:250px;dialogHeight:200px;resizable:yes')
  }
</script>
</head>

<body>
<p>Modal dialog sample</p>

<input type="button" value="btn1" onclick="openModal();">

<a id="lnk1" href="javascript:openModal()">lnk1</a>
<div>

</div>
</body>
</html>