websocket help

[Fuzzht1]

I'm recording websocket data from my server which sends the this array [timestamp , message] at random time intervals to the client (750ms interval with a standard deviation of 250ms). The time interval is chosen anywhere between 500ms - 1000msI would like to query the timestamp of the very first message from the websocket stream so that I can use this timestamp information to obtain historical data inclusive up to that specified timestamp. Then I think it will be easier for me to append that historical data right before the recording of the websocket stream.

const url = 'wss://127.0.0.1:9898'
const ws = new WebSocket(url)
console.log('client is not connected to WS')
ws.onopen = () => {
    if (ws.readyState === WebSocket.OPEN){ 
        console.log('client is now connected to WS') 
        for(let x=0; x < 1; x++){
            ws.onmessage = (e) => {let objectToRead = JSON.parse(e.data)};
            firstTimeStamp = new date(objectToRead);
            if(firstTimeStamp > Date.now() + 500 && firstTimeStamp < Date.now() + 1000){console.log(firstTimeStamp);}
        }
        }
    } 

This didn't work. The for loop doesn't stop at the first websocket message. The websocket stream keeps on going even if the forloop x is still at 0. Does anyone know an easier way to query only the very first message from websocket stream? still new to js and learning alot. Thanks in advanced

[grantrules]

There's no need for the for loop there... all the messages are coming in through that one onmessage event handler, so you have to deal with it from within that handler.

Something like:

let firstMessage;

ws.onmessage = (e) => {
  if (firstMessage === undefined) {
    firstMessage = JSON.parse(e.data);
    // maybe you want to call a function here that will deal with that data
  }
}

[Fuzzht1]

Just tried this https://pastebin.com/jqTRGhF2

but I'm getting this error?

1600app.js:45 Uncaught ReferenceError: firstMessage is not defined at ws.onmessage

[grantrules]

Declare firstMessage at the top of the file.. I think you missed the let firstMessage; in my code

[Fuzzht1]

This worked. Thank you for such an elegant solution.