The writable read-only property of the SerialPort interface returns a WritableStream for sending data to the device connected to the port. Chunks written to this stream must be instances of ArrayBuffer, TypedArray, or DataView. This property is non-null as long as the port is open and has not encountered a fatal error.

A WritableStream

The following example shows how to write a string to a port. A TextEncoder converts the string to a Uint8Array before transmission.

const encoder = new TextEncoder();
const writer = port.writable.getWriter();
await writer.write(encoder.encode("PING"));
writer.releaseLock();