Add class to class .flex-viewport

I have successfully added class .c to class .woocommerce-product-gallery__wrapper and class .d to class .woocommerce-product-gallery__image but I cannot add 2 classes .a and .b to class .flex-viewport. Here is the code I used. How can I add any 2 classes along with .flex-viewport class using javascript

add_action('wp_footer','test',99);
function test(){
if ( is_product() ) {
    ?>
		<script>
		jQuery(document).ready(function( $ ){
			jQuery('.flex-viewport').addClass('a b');
			jQuery('.woocommerce-product-gallery__wrapper').addClass('c');
			jQuery('.woocommerce-product-gallery__image').addClass('d');
		});
		</script>
    <?php
}
}