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<!DOCTYPE html>
<html>
<body>
<input type="week" id="myWeek"><br><br>
<button onclick="disableBtn()">Disable Week Field</button>
<button onclick="undisableBtn()">Undisable Week Field</button>
<script>
function disableBtn() {
  document.getElementById("myWeek").disabled = true;
}
function undisableBtn() {
  document.getElementById("myWeek").disabled = false;
}
</script>
</body>
</html>