WebSocket latency metric

I’m trying to benchmark a WebSocket echo server based on latency. My goal is to send as many messages as possible for 1 minute using X concurrent connections. I have written the following script:

import { WebSocket } from "k6/experimental/websockets";
import { Trend } from "k6/metrics";

export const options = {
  vus: __ENV.TOTAL_CLIENT,
  duration: "1m",
};

const url = __ENV.WS_URL;
const data = open(__ENV.DATA_FILE);
const duration = 60000; // 60s

const latency = new Trend("latency", true);

export default function () {
  const ws = new WebSocket(url);
  let start;

  ws.onopen = () => {
    const send = setInterval(() => {
      start = Date.now();
      ws.send(data);
    }, 1);

    ws.onmessage = (_) => {
      latency.add(Date.now() - start);
    };

    const close = setTimeout(() => {
      clearInterval(send);
      ws.close();
    }, duration);

    ws.onclose = () => {
      clearTimeout(close);
    };
  };
}

I also got the latency metric in the result:

     data_received.........: 86 MB 1.4 MB/s
     data_sent.............: 86 MB 1.4 MB/s
     iteration_duration....: avg=1m0s     min=1m0s     med=1m0s     max=1m0s     p(90)=1m0s     p(95)=1m0s   
     iterations............: 2     0.033332/s
     latency...............: avg=285.92µs min=0s       med=0s       max=2ms      p(90)=1ms      p(95)=1ms    
     vus...................: 2     min=2         max=2
     vus_max...............: 2     min=2         max=2
     ws_connecting.........: avg=552.37µs min=532.21µs med=552.37µs max=572.52µs p(90)=568.49µs p(95)=570.5µs
     ws_msgs_received......: 83159 1385.940918/s
     ws_msgs_sent..........: 83163 1386.007582/s
     ws_session_duration...: avg=1m0s     min=1m0s     med=1m0s     max=1m0s     p(90)=1m0s     p(95)=1m0s   
     ws_sessions...........: 2     0.033332/s

but i doubt that this is the correct way to get the latency metric, am i wrong? is there any other way?

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