FORQY — Custom Settings of the jQuery UI Datepicker

functions.php

<?php

if ( ! function_exists( 'THEME_scripts_datepicker' ) ) {

	/**
	 * Custom Settings of the jQuery UI Datepicker
	 * @url https://api.jqueryui.com/datepicker/
	 */
	function THEME_scripts_datepicker() {

		$datepicker = '
			(function ($) {
				"use strict";
				// Allow selection only two days in advance
				$(".js-datepicker").datepicker("option", "maxDate", "+2D");
                
				// Disable selection of the Sundays and Mondays
				$(".js-datepicker").datepicker("option", "beforeShowDay", function(date) {
					var day = date.getDay();
					return [day > 1,""]; // 0 = sunday, 1 = monday
				});
			}(jQuery));
		';

		wp_add_inline_script( 'jquery-ui-datepicker', $datepicker );

	}

	add_action( 'wp_enqueue_scripts', 'THEME_scripts_datepicker', 90 );

}