javascript – Onchange behavior of Safari input type=”date”

I have a 700-line HTML/JavaScript page that, among other things, validates dates. It works on Chrome, Edge, and Firefox, and fails on iOS Safari 14.4 because the change event on input type="date" fires before the user makes a selection. A mostly-minimal example is this:

<form name="test" >
<input type="date" name="date1" id="date1"><br>
<br>
</form>
<button id="ckValue">Check Value</button>
<script type="text/javascript">
document.getElementById("date1").addEventListener("change",dtChange);
document.getElementById("ckValue").addEventListener("click",getValue);
function dtChange(evt) {
    var val=document.getElementById("date1").value;
    alert('Change event signaled; value='+val);
}
function getValue() {
    var val=document.getElementById("date1").value;
    alert("Value of date ="+val);
}
</script>

It’s in a fiddle here: https://jsfiddle.net/1jnqf5aL/1/

In this example run on Safari, when the form is initially loaded and the date item is touched/tapped, the change event fires immediately and the value of the input item is the current date. My application detects the change event and emits a “Departure date must be in the future” error message before the user has had an opportunity to select a date.

With other browsers, e.g. Chrome, Edge, Firefox, the change event does not fire until the user has selected a date in the calendar form.

I can make Safari behave, sort-of, by providing an initial value= attribute on the input element where the value is the current date in ISO 8601 format. The trouble with that is, the current date is not a valid date in this application, so I don’t want to show it to the user of the application. Browser sniffing will fail if/when Safari is changed to behave similarly to other browsers.

My question: How can I accommodate, or “program around” this behavior of Safari without browser sniffing? Or, have I missed something obvious and fundamental?