Woocommerce Ajax Add To Cart Button

wc_ajax_add_to_cart.php

<?php
//AJAX ADD TO CART BUTTON

$product_id = 143;
if( !my_custom_cart_contains( $product_id ) ) {
	?>
	<button class="my-custom-add-to-cart-button" data-product-id="<?php echo $product_id; ?>">add to cart</button>
	<?php
} else {
	?>
	<button class="my-custom-add-to-cart-button" data-product-id="<?php echo $product_id; ?>" disabled="disabled">added to cart</button>
	<?php
}
?>




<?php
//ADD TO CART FUNCTION

add_action('wp_footer', 'my_custom_wc_button_script');
function my_custom_wc_button_script() {
	?>
	<script>
		jQuery(document).ready(function($) {
			var ajaxurl = "<?php echo esc_attr( admin_url( 'admin-ajax.php' ) ); ?>";
			$( document.body).on('click', '.my-custom-add-to-cart-button', function(e) {
				e.preventDefault();
				var $this = $(this);
				if( $this.is(':disabled') ) {
					return;
				}
				var id = $(this).data("product-id");
				var data = {
					action     : 'my_custom_add_to_cart',
					product_id : id
				};
				$.post(ajaxurl, data, function(response) {
					if( response.success ) {
						$this.text("added to cart");
						$this.attr('disabled', 'disabled');
						$( document.body ).trigger( 'wc_fragment_refresh' );
					}
				}, 'json');
			})
		});
	</script>
	<?php
}
add_action('wp_ajax_my_custom_add_to_cart', "my_custom_add_to_cart");
add_action('wp_ajax_nopriv_my_custom_add_to_cart', "my_custom_add_to_cart");
function my_custom_add_to_cart() {
	$retval = array(
		'success' => false,
		'message' => ""
	);
	if( !function_exists( "WC" ) ) {
		$retval['message'] = "woocommerce not installed";
	} elseif( empty( $_POST['product_id'] ) ) {
		$retval['message'] = "no product id provided";
	} else {
		$product_id = $_POST['product_id'];
		if( my_custom_cart_contains( $product_id ) ) {
			$retval['message'] = "product already in cart";
		} else {
			$cart = WC()->cart;
			$retval['success'] = $cart->add_to_cart( $product_id );
			if( !$retval['success'] ) {
				$retval['message'] = "product could not be added to cart";
			} else {
				$retval['message'] = "product added to cart";
			}
		}
	}
	echo json_encode( $retval );
	wp_die();
}
function my_custom_cart_contains( $product_id ) {
	$cart = WC()->cart;
	$cart_items = $cart->get_cart();
	if( $cart_items ) {
		foreach( $cart_items as $item ) {
			$product = $item['data'];
			if( $product_id == $product->id ) {
				return true;
			}
		}
	}
	return false;
}

//Created By Adhersh M Nair
//Reference: https://gist.github.com/gschoppe/46f37a75841738ab86ef3039fc8010e6#file-wc_ajax_add_to_cart-php