Add custom javascripts or php action on WooCommerce Thank you page after order completes

xlwcty_add_custom_action_thankyou.php

<?php
/**
 * This is a PHP code, so should be wrapped inside PHP
 * Like we added here.
 * If PHP is already open then don't include above <?php open tag
 */
/**
 * Adding custom javascripts or php action on WooCommerce Thank you page
 * Works with WooCommerce 3.0 or above
 */
add_action( "woocommerce_thankyou", "xlwcty_thank_you_script", 20 );

if ( ! function_exists( 'xlwcty_thank_you_script' ) ) {
	function xlwcty_thank_you_script( $order_id ) {
		if ( $order_id > 0 ) {
			$order = wc_get_order( $order_id );
			if ( $order instanceof WC_Order ) {
				$order_id               = $order->get_id(); // order id
				$order_key              = $order->get_order_key(); // order key
				$order_total            = $order->get_total(); // order total
				$order_currency         = $order->get_currency(); // order currency
				$order_payment_method   = $order->get_payment_method(); // order payment method
				$order_shipping_country = $order->get_shipping_country(); // order shipping country
				$order_billing_country  = $order->get_billing_country(); // order billing country
				$order_status           = $order->get_status(); // order status
				/**
				 * full list methods and property that can be accessed from $order object
				 * https://docs.woocommerce.com/wc-apidocs/class-WC_Order.html
				 */
				?>
                <script type="text/javascript">
                    // write custom action here
                </script>
				<?php
			}
		}
	}
}

/**
 * This code execute inside head tag
 */
add_action( "wp_head", "xlwcty_thank_you_header_script", 20 );

if ( ! function_exists( 'xlwcty_thank_you_header_script' ) ) {
	function xlwcty_thank_you_header_script() {
		if ( function_exists( 'is_order_received_page' ) && is_order_received_page() && isset( $_GET['order_id'] ) ) {
			$order_id = $_GET['order_id'];
			$order    = wc_get_order( $order_id );
			if ( $order instanceof WC_Order ) {
				$order_id               = $order->get_id(); // order id
				$order_key              = $order->get_order_key(); // order key
				$order_total            = $order->get_total(); // order total
				$order_currency         = $order->get_currency(); // order currency
				$order_payment_method   = $order->get_payment_method(); // order payment method
				$order_shipping_country = $order->get_shipping_country(); // order shipping country
				$order_billing_country  = $order->get_billing_country(); // order billing country
				$order_status           = $order->get_status(); // order status
				/**
				 * full list methods and property that can be accessed from $order object
				 * https://docs.woocommerce.com/wc-apidocs/class-WC_Order.html
				 */
				?>
                <script type="text/javascript">
                    // write custom action here
                </script>
				<?php
			}
		}
	}
}