<!DOCTYPE html>
<html>
<body>
<form name="ipForm">
UserName : <input type="text" name="userName">
</form>
<button id="html">get innerHTML</button>
<script type='text/javascript'>
document.getElementById("html").onclick = function() {
var elems = document.getElementsByName("ipForm")[0].getElementsByTagName("input");
for(var i = 0; i < elems.length; i++) {
elems[i].setAttribute("value", elems[i].value);
}
console.log(document.getElementsByName("ipForm")[0].innerHTML);
}
</script>
</body>
</html>