<html>
<body>
<input type="week" id="myWeek" value="1995-W35">
<p>Click the button to change the default value of the week field.</p>
<button type="button" onclick="myFunction()">Try it</button>
<script>
function myFunction() {
document.getElementById("myWeek").defaultValue = "2014-W43";
}
</script>
</body>
</html>