files/en-us/web/api/serialport/close/index.md
{{APIRef("Web Serial API")}}{{SecureContext_Header}}{{SeeCompatTable}}{{AvailableInWorkers("window_and_dedicated")}}
The SerialPort.close() method of the {{domxref("SerialPort")}} interface returns a {{jsxref("Promise")}} that resolves when the port closes.
close()
None.
A {{jsxref("Promise")}}.
close() closes the serial port if previously-locked {{domxref("SerialPort.readable")}} and {{domxref("SerialPort.writable")}} members are unlocked, meaning the releaseLock() methods have been called for their respective reader and writer.
However, when continuously reading data from a serial device using a loop, the associated readable stream will always be locked until the reader encounters an error. In this case, calling reader.cancel() will force reader.read() to resolve immediately with { value: undefined, done: true } allowing the loop to call reader.releaseLock().
// Without transform streams.
let keepReading = true;
let reader;
async function readUntilClosed() {
while (port.readable && keepReading) {
reader = port.readable.getReader();
try {
while (true) {
const { value, done } = await reader.read();
if (done) {
// reader.cancel() has been called.
break;
}
// value is a Uint8Array.
console.log(value);
}
} catch (error) {
// Handle error...
} finally {
// Allow the serial port to be closed later.
reader.releaseLock();
}
}
await port.close();
}
const closedPromise = readUntilClosed();
document.querySelector("button").addEventListener("click", async () => {
// User clicked a button to close the serial port.
keepReading = false;
// Force reader.read() to resolve immediately and subsequently
// call reader.releaseLock() in the loop example above.
reader.cancel();
await closedPromise;
});
Closing a serial port is more complicated when using transform streams. See Close a serial port for guidance.
{{Specifications}}
{{Compat}}