Class: WebUsbTransport

WebUSB transport for browser environments.

Defaults to interface 0 — the same default as Node's UsbTransport. Pass { interfaceNumber } to claim a different interface; this is needed for composite devices like the LabelWriter 450 Duo, which exposes one interface per engine. Callers obtain a USBDevice via navigator.usb.requestDevice() (prompts the user) or navigator.usb.getDevices() (previously paired).

Implements

• Transport

Accessors

connected

Get Signature

get connected(): boolean;

Whether the transport is currently connected.

Returns

boolean

Implementation of

Transport.connected

Methods

close()

close(): Promise<void>;

Close the connection.

Always safe to call multiple times. Always await the result.

Returns

Promise<void>

Implementation of

Transport.close

---

read()

read(length: number, timeout?: number): Promise<Uint8Array>;

Read bytes from the printer.

Buffers until length bytes are available or the timeout fires.

BLE implementations: there is no "read N bytes" primitive in BLE. Implementations must buffer incoming GATT notifications internally and satisfy read() calls from that buffer. Document this in your transport class — every BLE implementation must handle buffering consistently so drivers get the same pull-based API on every transport.

Parameters

Parameter	Type
length	number
timeout?	number

Returns

Promise<Uint8Array>

Throws

TransportTimeoutError on timeout.

Throws

TransportClosedError if the transport is closed mid-read.

Implementation of

Transport.read

---

write()

write(data: Uint8Array): Promise<void>;

Send bytes to the printer.

Parameters

Parameter	Type
data	Uint8Array

Returns

Promise<void>

Implementation of

Transport.write

---

fromDevice()

static fromDevice(device: USBDevice, options?: WebUsbOpenOptions): Promise<WebUsbTransport>;

Wrap an already-selected USBDevice.

Opens the device, selects the requested configuration if it is not already active, claims the requested interface, and resolves the bulk IN / OUT endpoint numbers from that interface descriptor. Use this when the USBDevice came from navigator.usb.getDevices() (previously paired devices) or from external code.

Parameters

Parameter	Type
device	USBDevice
options?	WebUsbOpenOptions

Returns

Promise<WebUsbTransport>

---

request()

static request(filters: USBDeviceFilter[], options?: WebUsbOpenOptions): Promise<WebUsbTransport>;

Show the browser's USB picker and wrap the selected device.

Parameters

Parameter	Type	Description
filters	USBDeviceFilter[]	USB device filters (typically { vendorId, productId } pairs built by buildUsbFilters).
options?	WebUsbOpenOptions	Optional interface/configuration selection.

Returns

Promise<WebUsbTransport>