# Using services

To use services, add services as third parameter to your event handler.

E.g., if you want to use services from within the accounting.invoice.issued event handler, use the following code:

const when = {
  'accounting.invoice.issued' (invoices, event, services, mark) {
    // ...
    mark.asDone();
  }
};

# Reading other lists

Sometimes you need to read another list, e.g. to decide what to update. For that use the app service, access the list, and call the read or readOne function.

E.g., if you want to read another invoice from the accounting.invoice.issued event handler, use the following code:

const when = {
  'accounting.invoice.issued' (invoices, event, services, mark) {
    const app = services.get('app');

    app.lists.invoices.readOne({
      where: { id: '664745ac-808a-4c16-8420-f43d9deeee04' }
    }).
      failed(err => {
        // ...
      }).
      finished(otherInvoice => {
        // ...
        mark.asDone();
      });
  }
};

# Writing log output

To write JSON-formatted log output use the logger service. Internally this service uses flaschenpost. For details on how to use flaschenpost see its documentation.

E.g., to log messages from within the accounting.invoice.issued event handler, use the following code:

const when = {
  'accounting.invoice.issued' (invoices, event, services, mark) {
    const logger = services.get('logger');

    logger.info('Handling an issued invoice...');

    // ...
    mark.asDone();
  }
};