Set a specific default stock quantity on all WooCommerce new products

For “New” simple products on admin, the following embedded jQuery script will:

• trigger and enable “Stock management” at product level,
• set the “Stock quantity” to “1”,
• set the “Low stock threshold” to “0”.

The code:

add_action( 'admin_footer', 'new_product_stock_default_setting' );
function new_product_stock_default_setting() {
    global $pagenow, $post_type;

    // Targeting new product page (admin)
    if( $pagenow === 'post-new.php' && $post_type === 'product' ) :
    ?>
    <script>
    jQuery(function($){
        var a="#inventory_product_data input#";

        // Set Manage Stock and trigger event to show other related fields
        $(a+'_manage_stock').prop('checked', true).change();
        $(a+'_stock').val('1'); // Set Stock quantity to "1"
        $(a+'_low_stock_amount').val('0'); // Set Low stock threshold to "0"
    });
    </script>
    <?php
    endif;
}

Code goes in functions.php file of your active child theme (or active theme). Tested and works.