How do I send messages on a timer with websockets - node.js

Question

I have the following node.js code
const WebSocket = require("ws");
const db = require('./db')
const wss = new WebSocket.Server({port: 5000});
wss.on("connection", ws => {
console.log("New Client Connected!");
ws.on("message", data => {
console.log(data);
let interval = setInterval(()=> getSelPos(ws), 2000);
});
ws.on("close", () => {
console.log("Client has Disconnected");
});
});
const getSelPos = async(ws) =>{
try {
const result = await db.pool.query("select value from db.tags where tag in ('1006', '1004', '1002')");
ws.send({selector: result[2].value.toString(), pressure: result[1].value.toString(), temperature: result[0].value.toString()});
console.log(result);
} catch (err) {
throw err;
}
}
My intention is to perform an initial handshake with my React code, then once a message is received from React (a confirmation of the connection opening), I start a 2 second interval to send database updates to my react component data. However this code currently doesn't work. I'm not sure how to fix it now. Any ideas?
EDIT: Here is my code on the other end for testing purposes currently:
const ws = new WebSocket("ws://localhost:5000");
ws.addEventListener("open", () => {
console.log("We are connected!");
ws.send("Hello!");
});
ws.addEventListener("message", ({data}) => {
console.log(data);
});
EDIT 2:
Console output I got was:
New Client Connected!
<Buffer 48 65 6c 6c 6f 21>
(node:16492) UnhandledPromiseRejectionWarning: TypeError [ERR_INVALID_ARG_TYPE]: The first argument must be of type string or an instance of Buffer, ArrayBuffer, or Array or an Array-like Object. Received an instance of Object
at Function.from (buffer.js:330:9)
at toBuffer (my-path\node_modules\ws\lib\buffer-util.js:95:18)
at Sender.send (my-path\node_modules\ws\lib\sender.js:270:17)
at WebSocket.send (my-path\node_modules\ws\lib\websocket.js:423:18)
at getSelPos (my-path\server.js:22:12)
at processTicksAndRejections (internal/process/task_queues.js:95:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:16492) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:16492) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Answer 1

Looking at the error, it seems like you are using the socket instance ws in your getSelPos function but the function doesn't have access to it. Pass the instance to the function when you call it and it should work:
wss.on("connection", ws => {
console.log("New Client Connected!");
ws.on("message", data => {
console.log(data);
let interval = setInterval(()=> getSelPos(ws), 2000);
});
// rest of the function
});
const getSelPos = async(ws) =>{
// Use socket instance
}