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Outgoing Transform ​

Problem ​

You need one deterministic policy for application messages without continuation middleware that can call next() repeatedly or leave a send outcome implicit.

Solution ​

Use transform to return the serialized message shape or null to filter it.

ts
import { createPulse } from '@vielzeug/pulse';

type ClientEvents = {
  'chat:send': { text: string };
  'debug:trace': { detail: string };
};

const pulse = createPulse<{}, ClientEvents>('wss://api.example.com/ws', {
  transform: (message) => {
    if (message.event.startsWith('debug:')) return null;

    return {
      ...message,
      payload: { sentAt: Date.now(), value: message.payload },
    };
  },
});

await pulse.connect();
pulse.send('chat:send', { text: 'Hello!' });
pulse.send('debug:trace', { detail: 'filtered' });
pulse.dispose();

Pitfalls ​

  • transform is synchronous. Complete asynchronous policy decisions before calling send().
  • Return null to filter. Every other result is serialized and sent.
  • Internal frames bypass the transform. Reconnect, heartbeat, room, and presence protocol frames remain reliable.