Add quantity button and ajax functionality to add to cart button on product archive page.

add-to-cart.php

<?php
/**
 * Custom Loop Add to Cart.
 *
 * Template with quantity and ajax.
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly.

global $product;
?>

<?php if ( ! $product->is_in_stock() ) : ?>

    <a href="<?php echo apply_filters( 'out_of_stock_add_to_cart_url', get_permalink( $product->id ) ); ?>" class="button"><?php echo apply_filters( 'out_of_stock_add_to_cart_text', __( 'Read More', 'woocommerce' ) ); ?></a>

<?php else : ?>

    <?php
        $link = array(
            'url'   => '',
            'label' => '',
            'class' => ''
        );

        switch ( $product->product_type ) {
            case "variable" :
                $link['url']    = apply_filters( 'variable_add_to_cart_url', get_permalink( $product->id ) );
                $link['label']  = apply_filters( 'variable_add_to_cart_text', __( 'Select options', 'woocommerce' ) );
            break;
            case "grouped" :
                $link['url']    = apply_filters( 'grouped_add_to_cart_url', get_permalink( $product->id ) );
                $link['label']  = apply_filters( 'grouped_add_to_cart_text', __( 'View options', 'woocommerce' ) );
            break;
            case "external" :
                $link['url']    = apply_filters( 'external_add_to_cart_url', get_permalink( $product->id ) );
                $link['label']  = apply_filters( 'external_add_to_cart_text', __( 'Read More', 'woocommerce' ) );
            break;
            default :
                if ( $product->is_purchasable() ) {
                    $link['url']    = apply_filters( 'add_to_cart_url', esc_url( $product->add_to_cart_url() ) );
                    $link['label']  = apply_filters( 'add_to_cart_text', __( 'Add to cart', 'woocommerce' ) );
                    $link['class']  = apply_filters( 'add_to_cart_class', 'add_to_cart_button' );
                } else {
                    $link['url']    = apply_filters( 'not_purchasable_url', get_permalink( $product->id ) );
                    $link['label']  = apply_filters( 'not_purchasable_text', __( 'Read More', 'woocommerce' ) );
                }
            break;
        }

        // If there is a simple product.
        if ( $product->product_type == 'simple' ) {
            ?>
            <form action="<?php echo esc_url( $product->add_to_cart_url() ); ?>" class="cart" method="post" enctype="multipart/form-data">
                <?php
                    // Displays the quantity box.
                    woocommerce_quantity_input();

                    // Display the submit button.
                    echo sprintf( '<button type="submit" data-product_id="%s" data-product_sku="%s" data-quantity="1" class="%s button product_type_simple">%s</button>', esc_attr( $product->id ), esc_attr( $product->get_sku() ), esc_attr( $link['class'] ), esc_html( $link['label'] ) );
                ?>
            </form>
            <?php
        } else {
          echo apply_filters( 'woocommerce_loop_add_to_cart_link', sprintf('<a href="%s" rel="nofollow" data-product_id="%s" data-product_sku="%s" class="%s button product_type_%s">%s</a>', esc_url( $link['url'] ), esc_attr( $product->id ), esc_attr( $product->get_sku() ), esc_attr( $link['class'] ), esc_attr( $product->product_type ), esc_html( $link['label'] ) ), $product, $link );
        }

    ?>

<?php endif; ?>

functions.php

<?php

function cs_wc_loop_add_to_cart_scripts() {
    if ( is_shop() || is_product_category() || is_product_tag() || is_product() ) : ?>

<script>
    jQuery(document).ready(function($) {
        $(document).on( 'change', '.quantity .qty', function(event) {
            $(this).parent('.quantity').siblings('.add_to_cart_button').attr('data-quantity', $(this).val());
        });

        // The purpose is if the quantity is zero, then we should not trigger the click event of the button
        $(document).on( 'click', '.add_to_cart_button', function(event) {
            if($(this).siblings(".quantity").find(".qty").val() <= 0){
                event.stopImmediatePropagation();
                return false;
            }
        });
    });
</script>

    <?php endif;
}

add_action( 'wp_footer', 'cs_wc_loop_add_to_cart_scripts' );

Add bugfix for the behavior that adds a product even if the quantity is set to zero.