SolidJS•2mo ago

Reactivity resulting from updates in a websocket event listener

I am struggling to understand why setting a signal in an event listener is not driving re-rendering for the signal. In the code below I observe reactivity for count2 (that is set in the setInterval callback), but not for count (that is set when a message is received on the websocket). I can see from the console.log in the message event handler that the values passed to setCount are changing. So my expectation is that the rendered value should change. I don't doubt that the reason for this is covered somewhere in the docs. I suspect that I'm simply misreading or misunderstanding something.

import { JSX, createEffect, createSignal } from 'solid-js';

interface Message {
  count: number;
}

export default function SomeComponent(): JSX.Element {
  const [count, setCount] = createSignal(0);
  const [count2, setCount2] = createSignal(0);

  createEffect(() => {
    console.log('count', count());
    console.log('count2', count2());
  });

  const ws = new WebSocket('ws://localhost:3000/_ws');
  ws.addEventListener('message', (ev: MessageEvent) => {
    const message: Message = ev.data;
    console.log('message', message);
    setCount(message.count);
  });

  setInterval(() => {
    setCount2(count2() + 1);
  }, 1000);

  return (
    <div>
      <div>count : {count()}</div>
      <div>count2 : {count2()}</div>
    </div>
  );
}

import { JSX, createEffect, createSignal } from 'solid-js';

interface Message {
  count: number;
}

export default function SomeComponent(): JSX.Element {
  const [count, setCount] = createSignal(0);
  const [count2, setCount2] = createSignal(0);

  createEffect(() => {
    console.log('count', count());
    console.log('count2', count2());
  });

  const ws = new WebSocket('ws://localhost:3000/_ws');
  ws.addEventListener('message', (ev: MessageEvent) => {
    const message: Message = ev.data;
    console.log('message', message);
    setCount(message.count);
  });

  setInterval(() => {
    setCount2(count2() + 1);
  }, 1000);

  return (
    <div>
      <div>count : {count()}</div>
      <div>count2 : {count2()}</div>
    </div>
  );
}

1 Reply

pekim•2mo ago

It probably doesn't help that I've struggled to find the right search terms when looking in the docs and in discord. Solved : The problem was completely unrelated to Solid, and entirely down to my own silliness. The type of ev.data is a string, and I was coercing it to an object.

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Reactivity resulting from updates in a websocket event listener