Use drupal_add_js($var, 'setting') instead of drupal_add_js('js_var = ' . $php_var . ';', 'inline')

Instead of:

drupal_add_js('uc_store_credit_hide_method = '. variable_get('uc_store_credit_hide_method', 0) .';', 'inline');
drupal_add_js('uc_store_credit_user_total = '. uc_store_credit_user_total() .';', 'inline');
drupal_add_js('uc_store_credit_cart_total = '. uc_store_credit_cart_total() .';', 'inline');
drupal_add_js('uc_store_credit_line_item_rate = '. variable_get('uc_store_credit_conversion_rate', 100) .';', 'inline');
drupal_add_js("uc_store_credit_subtotal_string = '". t('Subtotal') ."';", 'inline');

Use:

drupal_add_js(
  array(
    'uc_store_credit' => array(
      'hide_method' => variable_get('uc_store_credit_hide_method', 0),
      'user_total' => uc_store_credit_user_total(),
      'cart_total' => uc_store_credit_cart_total(),
      'line_item_rate' => variable_get('uc_store_credit_conversion_rate', 100),
      'subtotal_string' => t('Subtotal'),
    ),
  ),
  'setting'
);

Your variables are then available as Drupal.settings.uc_store_credit.hide_method instead.