Check if date is in the past without submitting form

Question

I have this code that I want to check if a date is in the past. I want to check it as soon as the date is entered, before form submission.

<input id="datepicker" onchange="checkDate()" required class="datepicker-input" type="text" data-date-format="yyyy-mm-dd" >

<script type="text/javascript">
 function checkDate() {
   var selectedDate = document.getElementById('datepicker').value;
   var now = new Date();
   if (selectedDate < now) {
    alert("Date must be in the future");
   }
 }
</script>

This does not work, if I enter a date in the past (e.g. 2014-12-03) it does not display the alert.

Answer 1

All you need to do is convert the string produced by the <input> into a Date using the Date constructor new Date("2014-06-12")

 function checkDate() {
   var selectedText = document.getElementById('datepicker').value;
   var selectedDate = new Date(selectedText);
   var now = new Date();
   if (selectedDate < now) {
    alert("Date must be in the future");
   }
 }

<input id="datepicker" onchange="checkDate()" required class="datepicker-input" type="date" data-date-format="yyyy-mm-dd" >

Answer 2

The date() function returns a string. Try converting both dates to integers first using the Date.parse() function:

<input id="datepicker" onchange="checkDate()" required class="datepicker-input" type="text" data-date-format="yyyy-mm-dd" >

<script type="text/javascript">
   function checkDate() {
       var selectedDate = document.getElementById('datepicker').value;
       var now = new Date();
       var dt1 = Date.parse(now),
       dt2 = Date.parse(selectedDate);
       if (dt2 < dt1) {
            alert("Date must be in the future");
       }
 }
</script>