SerialPort: close() method

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Secure context: This feature is available only insecure contexts (HTTPS), in some or allsupporting browsers.

Experimental:This is anexperimental technology
Check theBrowser compatibility table carefully before using this in production.

Note: This feature is available inDedicated Web Workers.

TheSerialPort.close() method of theSerialPort interface returns aPromise that resolves when the port closes.

close() closes the serial port if previously-lockedSerialPort.readable andSerialPort.writable members are unlocked, meaning thereleaseLock() methods have been called for their respective reader and writer.

However, when continuously reading data from a serial device using a loop, the associatedreadable stream will always be locked until thereader encounters an error. In this case, callingreader.cancel() will forcereader.read() to resolve immediately with{ value: undefined, done: true } allowing the loop to callreader.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 usingtransform streams. SeeClose a serial port for guidance.