Panel User Scripts

Panel User Scripts Skill

The in-app TypeScript editor that lets users write custom message transformations.

Architecture

UserScripts Panel (Monaco editor)
    │
    ▼
UserScriptPlayer (wraps the base Player)
    │
    ├── Transformer Worker (compiles + reports diagnostics)
    │   └── TypeScript compiler (in-Worker)
    │
    └── Runtime Worker (sandboxed script execution)
        └── user code runs here (isolated)

Core Components

Script Lifecycle

1. User writes TypeScript in Monaco
2. On save: code is sent to the Transformer Worker for compilation
3. Transformer compiles TS → JS and reports diagnostics (errors/warnings)
4. On success: the JS bundle is sent to the Runtime Worker
5. During playback: messages on input topics → Runtime Worker → output messages
6. Output messages are injected into PlayerState as additional topics

Worker Naming Pattern

// unique name per instance — isolates workers per tab (no cross-tab sharing)
new SharedWorker(new URL("./transformerWorker/index", import.meta.url), {
  name: uuidv4(),
});

• SharedWorker is the worker type, but cross-tab instance reuse is disabled by unique naming.
• Within a single player lifetime, runtime workers are reused/pooled where possible.
• Each active script processor maps to an isolated runtime execution context.

Monaco Integration

• Full TypeScript language service (autocomplete, errors, hover)
• Custom Lichtblick script-API type definitions injected
• Diagnostics shown inline and in a panel below the editor

Script API

export const inputs = ["/camera/image"];
export const output = "/processed_image";

export default function transform(event: MessageEvent): OutputMessage {
  return {
    /* processed data */
  };
}

Performance Notes

• Script execution never blocks the main thread (Worker isolation)
• Unchanged scripts don't recompile (compilation caching)
• Only subscribed input topics are forwarded to the Worker
• Runtime errors in user code are contained — they don't crash the app
• Each Runtime Worker has its own heap (no cross-script interference)

Key Files

• packages/suite-base/src/panels/UserScriptEditor/
• packages/suite-base/src/players/UserScriptPlayer/index.ts
• packages/suite-base/src/players/UserScriptPlayer/transformerWorker/
• packages/suite-base/src/players/UserScriptPlayer/runtimeWorker/

Skills Reference

• For SharedWorker patterns: load web-workers skill