test.html

<head>
    <title>1902 TESTING PAGE</title>

    <style>
        #iframe_elememt {
            width: 90%;
            height: 500px;
            margin-top: 20px;
            display: block;
        }

        #iframe_url {
            height: 44px;
            width: 20%;
        }

        #button {
            height: 44px;
            width: 200px;
        }

    </style>

</head>
<body>
    <p>Set iframe url here:</p>
    <input type="text" id="iframe_url">
    <button type="button" id="button" onclick="loadIframe()">Load Iframe</button>


    <p>Iframe:</p>
    <iframe id="iframe_elememt"></iframe>

    <script type="text/javascript">

        function loadIframe()
        {
            var src = document.getElementById('iframe_url').value;
            document.getElementById('iframe_elememt').src = src;
        }
        
    </script>

</body>