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<!DOCTYPE html>
<html>
<body>
<p>Change the week of the week field, and then click the button below.</p>
<input type="week" id="myWeek" value="1995-W35">
<p>Note that the default value is not affected when you change the value of the week field.</p>
<button type="button" onclick="myFunction()">Try it</button>
  
<p id="demo"></p>
<script>
function myFunction() {
  var x = document.getElementById("myWeek");
  var defaultVal = x.defaultValue;
  var currentVal = x.value;
  
  if (defaultVal == currentVal) {
    document.getElementById("demo").innerHTML = "Default value and current value is the same: "
    + x.defaultValue + " and " + x.value
    + "<br>Change the value of the week field to see the difference!";
  } else {
    document.getElementById("demo").innerHTML = "The default value was: " + defaultVal
    + "<br>The new, current value is: " + currentVal;
  }
}
</script>
</body>
</html>