Adding an example of how to watch a serial port using Event Emitters and So…

examples/serial-port/client.ts

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+import { io } from "socket.io-client";
+
+const socket = io("ws://localhost:8080/", {});
+
+socket.on("connect", () => {
+  console.log(`connect ${socket.id}`);
+});
+
+socket.on("disconnect", () => {
+  console.log(`disconnect`);
+});
+
+socket.on("onDeviceDisconnected", () => {
+  console.log(`onDeviceDisconnected`);
+});
+socket.on("onDeviceConnected", () => {
+  console.log(`onDeviceConnected`);
+});

examples/serial-port/package.json

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+{
+  "name": "typescript-example",
+  "version": "1.0.0",
+  "description": "An example with TypeScript",
+  "private": true,
+  "scripts": {
+    "build": "tsc",
+    "start:server": "ts-node server.ts",
+    "start:client": "ts-node client.ts"
+  },
+  "author": "Damien Arrachequesne",
+  "license": "MIT",
+  "dependencies": {
+    "serialport": "^9.2.0",
+    "socket.io": "^4.0.0",
+    "socket.io-client": "^4.0.0",
+    "ts-node": "^9.0.0",
+    "typescript": "^4.0.5"
+  }
+}

examples/serial-port/server.ts

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+import { Server } from "socket.io";
+const SerialPort = require("serialport");
+const Readline = require("@serialport/parser-readline");
+const emitter = require("events").EventEmitter;
+
+const em = new emitter();
+const deviceName = "/dev/tty.usbserial-0001";
+
+const io = new Server(8080);
+
+let found = false;
+
+function findDevice() {
+  console.log("findDevice");
+  SerialPort.list()
+    .then(function (ports) {
+      // // iterate through ports
+      for (var i = 0; i < ports.length; i += 1) {
+        console.log("list", ports[i]);
+        if (ports[i].path === deviceName) {
+          console.log("device founded");
+          found = true;
+          em.emit("connected");
+          startDevice();
+          return;
+        }
+      }
+      if (!found) {
+        setTimeout(findDevice, 1000);
+      }
+    })
+    .catch(function (error) {
+      console.log("error on read port", error);
+    });
+}
+
+function startDevice() {
+  try {
+    const port = new SerialPort(deviceName, { baudRate: 9600 });
+    const parser = port.pipe(new Readline({ delimiter: "\n" })); // Read the port data
+
+    port.on("open", () => {
+      console.log("serial port open");
+    });
+
+    parser.on("data", (data) => {
+      console.log("got word from arduino:", data);
+      em.emit("onDataReceived", data);
+    });
+
+    port.on("close", function (err) {
+      console.log("Port closed."), err;
+      found = false;
+      em.emit("disconnect");
+      setTimeout(findDevice, 1000);
+    });
+  } catch (e) {
+    console.log("device not found ");
+  }
+}
+
+io.on("connect", (socket) => {
+  console.log(`connect ${socket.id}`);
+
+  if (found) {
+    socket.emit("onDeviceConnected");
+  } else {
+    socket.emit("onDeviceDisconnected");
+  }
+
+  em.on("disconnect", function (data) {
+    socket.emit("onDeviceDisconnected");
+  });
+  em.on("connected", function (data) {
+    socket.emit("onDeviceConnected");
+  });
+  em.on("onDataReceived", function (data) {
+    socket.emit("onDataReceived", data);
+  });
+
+  socket.on("disconnect", () => {
+    console.log(`disconnect ${socket.id}`);
+  });
+});
+
+console.log("start program");
+findDevice();

examples/serial-port/tsconfig.json

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+{
+    "compilerOptions": {
+      "module": "commonjs",
+      "target": "es5"
+    },
+    "exclude": [
+      "node_modules"
+    ]
+  }