gistfile1.txt

/* ADD CUSTOM FIELDS TO VARIATION PRODUCT */

//Display Fields
add_action( 'woocommerce_product_after_variable_attributes', 'variable_fields', 10, 2 );
//JS to add fields for new variations
add_action( 'woocommerce_product_after_variable_attributes_js', 'variable_fields_js' );
//Save variation fields
add_action( 'woocommerce_process_product_meta_variable', 'save_variable_fields', 10, 1 );
add_action( 'woocommerce_process_product_meta_variable-subscription' , 'save_variable_fields' , 10 , 1 ) ;

/**
 * Create new fields for variations
 *
*/
function variable_fields( $loop, $variation_data ) {
?>
  
  <tr>
    <td>
      <?php
      // Textarea
      woocommerce_wp_textarea_input( 
        array( 
          'id'          => '_weightdesc['.$loop.']', 
          'label'       => __( 'Weight Description', 'woocommerce' ), 
          'placeholder' => '', 
          'description' => __( 'Enter the custom value here.', 'woocommerce' ),
          'value'       => $variation_data['_weightdesc'][0],
        )
      );
      ?>
    </td>
  </tr>
  
  <tr>
    <td>
      <?php
      // Hidden field
      woocommerce_wp_hidden_input(
      array( 
        'id'    => '_hidden_field['.$loop.']', 
        'value' => 'hidden_value'
        )
      );
      ?>
    </td>
  </tr>
<?php
}

/**
 * Create new fields for new variations
 *
*/
function variable_fields_js() {
?>
  
  <tr>
    <td>
      <?php
      // Textarea
      woocommerce_wp_textarea_input( 
        array( 
          'id'          => '_weightdesc[ + loop + ]', 
          'label'       => __( 'My Textarea', 'woocommerce' ), 
          'placeholder' => '', 
          'description' => __( 'Enter the custom value here.', 'woocommerce' ),
          'value'       => $variation_data['_weightdesc'][0],
        )
      );
      ?>
    </td>
  </tr>

<?php
}

/**
 * Save new fields for variations
 *
*/
function save_variable_fields( $post_id ) {
  if (isset( $_POST['variable_sku'] ) ) :

    $variable_sku          = $_POST['variable_sku'];
    $variable_post_id      = $_POST['variable_post_id'];
    
    // Textarea
    $_weightdesc = $_POST['_weightdesc'];
    for ( $i = 0; $i < sizeof( $variable_sku ); $i++ ) :
      $variation_id = (int) $variable_post_id[$i];
      if ( isset( $_weightdesc[$i] ) ) {
        update_post_meta( $variation_id, '_weightdesc', stripslashes( $_weightdesc[$i] ) );
      }
    endfor;
    
    
  endif;
}