Add start date to end date minimum in date input (Contact Form 7)

calendar-fix.js

var medieval = medieval || {};
var start; var end;

medieval.calendarFix = function ($) {

    "use strict";

    let initialize = function () {

        start = jQuery('input.date-start').first();
        end = jQuery('input.date-end').first();

        start.on('change', function() {
            let startDate = new Date($(this).val());
            startDate.setDate(startDate.getDate() + 3);
            let formattedStartDate = formatDate(startDate);
            end.attr('min', formattedStartDate);
        });

    };

    let formatDate = function (dateToFormat) {
        let year = dateToFormat.getFullYear();
        let month = dateToFormat.getMonth() + 1;
        if (month < 10) month = '0' + month;
        let day = dateToFormat.getDate();
        if (day < 10) day = '0' + day;
        return year + '-' + month + '-' + day;
    };

    return {
        init: function () {
            initialize();
        }
    };

}(jQuery);

jQuery(document).ready(function () {
    medieval.calendarFix.init();
});

functions.php

// Fix Calendar
add_action('wp_enqueue_scripts', function () {
    if (!is_front_page()) return;
    wp_enqueue_script('calendar-fix-js', get_stylesheet_directory_uri() . '/assets/js/calendar-fix.js', ['jquery'], null, true);
});