Disable Future Dates of Calendar from SharePoint Default Forms

//Add this script inside forms or page's script editor

<script src="//code.jquery.com/jquery-3.2.1.min.js" type="text/javascript"></script>
<script type="text/javascript">
var getSPDayDiff = function(date) {
return Math.round(Math.abs(( new Date(1601,0,1).getTime() - date.getTime())/( 24*60*60*1000 ) ) );
}
$(function () {
debugger;
var currentDate = new Date();
//currentDate.setMonth(currentDate.getMonth() + 1);
var minDay = getSPDayDiff(new Date());
var maxDay = getSPDayDiff(currentDate);

var datePicker=$("img[alt='Select a date from the calendar.']").parent();
var onclickStr=datePicker.attr("onclick");
//onclickStr=onclickStr.replace("minjday=109207", "minjday="+minDay);

        onclickStr=onclickStr.replace("minjday=109207", "minjday=109207");

onclickStr=onclickStr.replace("maxjday=2666269", "maxjday="+maxDay);
datePicker.attr("onclick",onclickStr);
});
</script>