<body>
<script src="oopif-input.js"></script>
<iframe style="width: 100px; height: 100px; position: absolute; top: 100px; left: 200px; border: 0;"></iframe>
<script>
var url = window.location.href;
url = url.replace(/a\.com/, "b.com");
url = url.replace(/oopif-input\.html/, "oopif-input-iframe.html");
document.querySelector('iframe').setAttribute('src', url);
</script>
</body>