Class: WebSerialTransport

Web Serial API transport.

Covers two physical pipes that look the same to the browser:

• OS-paired Bluetooth SPP devices (e.g. Brother QL-820NWB on Linux after pairing via the OS Bluetooth settings, or on Windows after the same). macOS dropped classic Bluetooth SPP — no serial route there.
• USB-to-serial adapters.

Browser only — Web Serial is Chrome/Edge (desktop and Android). The caller is responsible for pairing Bluetooth devices at the OS level first; the browser picker then lists them alongside wired ports.

Read path: the readable stream delivers chunks of arbitrary size. read(n) accumulates bytes until at least n are queued, matching the pattern used by TcpTransport and WebBluetoothTransport.

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

---

fromPort()

static fromPort(port: SerialPort, baudRate?: number): Promise<WebSerialTransport>;

Wrap an already-obtained SerialPort that is NOT yet open.

fromPort calls port.open() internally — pass the raw port returned by navigator.serial.getPorts() (previously authorized devices) or navigator.serial.requestPort(). Do not call port.open() yourself first.

Parameters

Parameter	Type	Default value
port	SerialPort	undefined
baudRate	number	DEFAULT_BAUD_RATE

Returns

Promise<WebSerialTransport>

---

request()

static request(options?: SerialPortRequestOptions, baudRate?: number): Promise<WebSerialTransport>;

Show the browser's serial-port picker and wrap the selected port.

Paired Bluetooth SPP devices appear alongside wired serial ports. For ports exposing a custom RFCOMM service class, pass allowedBluetoothServiceClassIds so the picker includes them — ports with standard SPP (UUID 0x1101) show up without a filter.

Parameters

Parameter	Type	Default value	Description
options?	SerialPortRequestOptions	undefined	Forwarded to navigator.serial.requestPort.
baudRate?	number	DEFAULT_BAUD_RATE	Default 9600. Ignored for Bluetooth SPP (RFCOMM handles flow control) but required by the Web Serial API.

Returns

Promise<WebSerialTransport>