Transform Node

The transform node executes a user-defined JavaScript function to reshape the message context before it continues down the pipeline or is broadcast.

When to Use

• Add computed fields to a message payload
• Remove or rename fields before broadcasting to clients
• Change the event name or metadata values
• Merge static data into every message

Configuration

* Provide exactly one of transformer or code.

JavaScript Context Object

Your function receives and must return a context object:

{
  metadata: {
    appId:   "your-app-id",
    channel: "chat-room",
    event:   "new-message"
  },
  data: {
    // message payload from the client or server
  },
  broadcasts: []  // do not modify directly
}

Return the full context object (modified as needed). Returning null or a non-object will cause the pipeline to error.

Examples

Add a server timestamp

export default function transform(context) {
  return {
    ...context,
    data: {
      ...context.data,
      serverTimestamp: Date.now(),
    }
  };
}

Remove a sensitive field

export default function transform(context) {
  const { password, ...safeData } = context.data;
  return { ...context, data: safeData };
}

Change the event name

export default function transform(context) {
  return {
    ...context,
    metadata: {
      ...context.metadata,
      event: 'processed-message',
    }
  };
}

Inline code style (no export)

return {
  ...context,
  data: { ...context.data, processed: true }
};

Runtime Limits

The runtime is QuickJS — a sandboxed JavaScript engine. ES2020 syntax is supported. Node.js built-ins (fs, path, http, etc.) are not available.

Bytecode Caching

Transforms are compiled to bytecode and cached in Redis. The first execution after a flow publish compiles the function; subsequent executions use cached bytecode for faster dispatch.

Next Steps

• Filter Node — filter messages before or after transforming
• Send to Channel Node — broadcast the transformed message
• Schema Validator Node — validate shape before transforming