Adding product to cart using ajax

Hi everyone,

I’m new to WordPress and Woocommerce, and I’m trying to add an item to the shopping cart with a button click, using ajax. So I have this code in php:

function add_product_to_cart() {
    $product_id = 5;
	$found = false;

	//check if product already in cart

	if (sizeof( WC()->cart->get_cart() ) > 0) {
	    foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
		    $_product = $values['data'];

			if ($_product->id == $product_id) {
			    $found = true;
				echo "found";
			}
		}

		if (!$found) {
		    WC()->cart->add_to_cart( $product_id );
			echo "added";
		}
	} 

	else {
	    WC()->cart->add_to_cart( $product_id );
		echo "added";
	}
}

The problem is that I cannot simply invoke it using ajax, since WC function is undefined. How do I do it then?

Thanks.

https://wordpress.org/plugins/woocommerce/