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

```html
<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>
```
Before comparing dates, they should be set to 0 hours. This would ensure difference between them is in multiples of 1 day.

```
const isPastDate = (date) => {
    const specificDate = new Date(date).setHours(0, 0, 0, 0);
    const today = new Date().setHours(0, 0, 0, 0);
    return specificDate < today;
}

console.log(isPastDate("2021-08-10T23:59:00"));

```