W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<body>

<p>Change the date and time of the datetime field, and then click the button below.</p>

<p>Note that the default value is not affected when you change the value of the datetime field.</p>

<button type="button" onclick="myFunction()">Try it</button>
  
<p><strong>Note:</strong> input elements with type="datetime-local" do not show as any datetime field/calendar in Firefox.</p>

</body>
</html>

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<!DOCTYPE html><html><body>​<p>Change the date and time of the datetime field, and then click the button below.</p>​<input type="datetime-local" id="myLocalDate" value="2014-11-16T15:25:33">​<p>Note that the default value is not affected when you change the value of the datetime field.</p>​<button type="button" onclick="myFunction()">Try it</button>  <p><strong>Note:</strong> input elements with type="datetime-local" do not show as any datetime field/calendar in Firefox.</p>​<p id="demo"></p>​<script>function myFunction() {  var x = document.getElementById("myLocalDate");  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 datetime 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>​