Restrict dates on jQuery UI Datepicker within WordPress/WooCommerce checkout

functions.php

<?php

if( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly


// AJAX request to disable days on calendar in checkout
add_action( 'wp_ajax_company_holidays', 'company_holidays_callback' );
add_action( 'wp_ajax_nopriv_company_holidays', 'company_holidays_callback' );
function company_holidays_callback() {
    $holidays = [];
    $currentYear = $limitYear = (int) date('Y');

    do {
        // New Years
        $x = date('N', strtotime("first day of january $currentYear"));
        $day = date('d', strtotime("first day of january $currentYear"));
        array_push($holidays, [1, (int) ($day + fri_or_mon($x)), $currentYear]);

        // President's Day
        $day = date('d', strtotime("third monday of february $currentYear"));
        array_push($holidays, [2, (int) $day, $currentYear]);

        // Good Friday
        $month = date('m', strtotime("-2 day", easter_date($currentYear)));
        $day = date('d', strtotime("-2 day", easter_date($currentYear)));
        array_push($holidays, [(int) $month, (int) $day, $currentYear]);
        
        // Memorial Day
        $day = date('d', strtotime("last Monday of May $currentYear"));
        array_push($holidays, [5, (int) $day, $currentYear]);

        // July 4th
        $x = (int) date('N', strtotime("3 day", strtotime("July $currentYear")));
        $day = (int) date('d', strtotime("3 day", strtotime("July $currentYear")));
        array_push($holidays, [7, $day, $currentYear]);

        // Labor Day
        $day = date('d', strtotime("first Monday of September $currentYear"));
        array_push($holidays, [9, (int) $day, $currentYear]);

        // Veteran's Day
        $x = date('N', strtotime("10 day", strtotime("November $currentYear")));
        $day = date('d', strtotime("10 day", strtotime("November $currentYear")));
        array_push($holidays, [11, (int) ($day + fri_or_mon($x)), $currentYear]);

        // Thanksgiving + Black Friday
        $day = date('d', strtotime("fourth Thursday of November $currentYear"));
        array_push($holidays, [11, (int) $day, $currentYear]);
        array_push($holidays, [11, (int) $day + 1, $currentYear]);

        // Xmas eve
        $day = date('d', strtotime("last day of December $currentYear"));
        $day = ((int) $day) - 7;
        array_push($holidays, [12, $day, $currentYear]);

        // Xmas
        $twenty_fifth = strtotime("-6 day", strtotime("last day of December $currentYear"));
        $x = date('N', $twenty_fifth);
        $day = date('d', $twenty_fifth);
        array_push($holidays, [12, $day + fri_or_mon($x), $currentYear]);
        $currentYear++;
    } while ($currentYear < $limitYear + 2);

    wp_send_json($holidays);
}

// Accepts a numerical value for the day of the week. Returns # of days to be added
function fri_or_mon($dayofweek) {
    if($dayofweek == 6) {
        // we get the previous Friday off
        return -1;
    }
    elseif($dayofweek == 7) {
        // we get the following Monday off
        return 1;
    }
    else {
        return 0;
    }
}

script.js

jQuery(document).ready( function() {
	function nationalDays(date) {
	    for (i = 0; i < natDays.length; i++) {
	      if (date.getMonth() === natDays[i][0] - 1
	          && date.getDate() === natDays[i][1] && date.getFullYear() === natDays[i][2]) {
	        return [false];
	      }
	    }
	  return [true];
	}

	function noWeekendsOrHolidays(date) {
	    var noWeekend = jQuery.datepicker.noWeekends(date);

	    if (noWeekend[0]) {
	        return nationalDays(date);
	    } else {
	        return noWeekend;
	    }
	}
	if(jQuery("#order_fulfillment_date").length) {
		var natDays = [];

	    jQuery.post(ajax_object.ajax_url, {action: 'company_holidays'}, function(response) {
			natDays = response;
		})
		.fail(function(response) {
			natDays = [];
			console.log("error with dates in calendar");
		});
	}
	// Datepicker on checkout
	jQuery("#order_fulfillment_date").datepicker({
		minDate: 1,
		maxDate: 365,
		beforeShowDay: noWeekendsOrHolidays
	});
});