hardwareAPI.js

// finding:
LabelPrinter.findPrinter(
  'usb',
  () => { /* handle printer found */ },
  () => { /* handle printer found finish */ },
  () => { /* handle printer error */ },
);

// printing:
LabelPrinter.printTest()
  .then(() => this.props.navigator.showLocalAlert('Test successful', successAlertStyle))
  .catch(() => this.props.navigator.showLocalAlert('Error occurred while printing test', errorAlertStyle))