WooCommerce custom function for Sort by Stock

wc_sort_by_stock

// Sort by stock on front end
add_filter( 'woocommerce_get_catalog_ordering_args', 'custom_woocommerce_get_catalog_ordering_args' );
function custom_woocommerce_get_catalog_ordering_args( $args ) {
  $orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );

    if ( 'stock' == $orderby_value ) {
        $args['orderby'] = 'meta_value';
        $args['order'] = 'asc';
        $args['meta_key'] = '_stock_status';
    }

    return $args;
}
add_filter( 'woocommerce_default_catalog_orderby_options', 'custom_woocommerce_catalog_orderby' );
add_filter( 'woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby' );
function custom_woocommerce_catalog_orderby( $sortby ) {
    $sortby['stock'] = 'Stock Status';
    return $sortby;
}