How to use the @ledgerhq/hw-transport-webusb.listen function in @ledgerhq/hw-transport-webusb

open: (id: string): ?Promise<*> => {
    if (id.startsWith("webble")) {
      const existingDevice = webbleDevices[id];
      return existingDevice
        ? TransportWebBLE.open(existingDevice)
        : TransportWebBLE.create();
    }
    return null;
  },

  disconnect: id =>
    id.startsWith("webble")
      ? Promise.resolve() // nothing to do
      : null,

  discovery: Observable.create(TransportWebUSB.listen).pipe(
    map(bleDevice => {
      const id = "webble|" + bleDevice.id;
      webbleDevices[id] = bleDevice;
      return {
        type: "add",
        id,
        name: bleDevice.name
      };
    })
  )
});

// provide a basic mecanism to stop polling when you leave the tab
// & immediately poll when you come back.
const addExtraPollingHooks = (schedulePoll, cancelPoll) => {
  function onWindowBlur() {

open: (id: string): ?Promise<*> => {
    if (id.startsWith("webusb")) {
      const existingDevice = webusbDevices[id];
      return existingDevice
        ? TransportWebUSB.open(existingDevice)
        : TransportWebUSB.create();
    }
    return null;
  },

  disconnect: id =>
    id.startsWith("webusb")
      ? Promise.resolve() // nothing to do
      : null,

  discovery: Observable.create(TransportWebUSB.listen).pipe(
    map(usbDevice => {
      const id = "webusb|" + usbDevice.vendorId + "_" + usbDevice.productId;
      webusbDevices[id] = usbDevice;
      return {
        type: "add",
        id,
        name: usbDevice.productName
      };
    })
  )
});

const webbleDevices = {};

registerTransportModule({
  id: "webble",