​

let port, reader, writer;

let serialActive = false;

​

async function getPort(baud = 9600) {

  let port = await navigator.serial.requestPort();

​

  // Wait for the serial port to open.

  await port.open({ baudRate: baud });

​

  // create read & write streams

  textDecoder = new TextDecoderStream();

  textEncoder = new TextEncoderStream();

  readableStreamClosed = port.readable.pipeTo(textDecoder.writable);

  writableStreamClosed = textEncoder.readable.pipeTo(port.writable);

​

  reader = textDecoder.readable

    .pipeThrough(new TransformStream(new LineBreakTransformer()))

    .getReader();

  writer = textEncoder.writable.getWriter();

​

  return { port, reader, writer };

}

​

class LineBreakTransformer {

  constructor() {

    // A container for holding stream data until a new line.

    this.chunks = "";

  }

​

  transform(chunk, controller) {

    // Append new chunks to existing chunks.

    this.chunks += chunk;

    // For each line breaks in chunks, send the parsed lines out.

    const lines = this.chunks.split("\r\n");

    this.chunks = lines.pop();

    lines.forEach((line) => controller.enqueue(line));

  }

​

  flush(controller) {

    // When the stream is closed, flush any remaining chunks out.

    controller.enqueue(this.chunks);

  }

}

​

async function setUpSerial() {

  noLoop();

  ({ port, reader, writer } = await getPort());

  serialActive = true;

  runSerial();

  loop();

}

​

async function runSerial() {

  try {

    while (true) {

      if (typeof readSerial === "undefined") {

        console.log("No readSerial() function found.");

        serialActive = false;

        break;

      } else {

        const { value, done } = await reader.read();

        if (done) {

          // Allow the serial port to be closed later.

          reader.releaseLock();

          break;

        }

        readSerial(value);

      }

    }

  } catch (e) {

    console.error(e);

  }

}

​

async function writeSerial(msg) {

  await writer.write(msg);

}

​