dash.js Agent Skills & AI Rules

# AGENTS.md

dash.js — DASH Industry Forum reference client. Pure JS (ES2020), ESM, Node >= 20.

## Gotchas

### Build & Test
- **`npm run build` skips tests/lint.** Use `npm run build-modern` for the full pipeline (clean + tsc + test + lint + webpack).
- **No per-file test runner.** All unit tests are bundled by Karma/webpack. Filter with `--grep`:
  ```bash
  npx karma start test/unit/config/karma.unit.conf.cjs --grep="EventBus"
  ```
- **Functional tests load from `dist/`**, not source. Build first.
- **Two entry points:** `index.js` (full) and `index_mediaplayerOnly.js` (lightweight). Public API changes may need both updated.
- **Dev builds fewer webpack bundles than prod.** See `build/webpack/common/webpack.common.base.cjs`.

### Architecture
- **Context = DI container.** Each `MediaPlayer` creates its own `context` object. All singletons are scoped to it: `EventBus(context).getInstance()`. This enables multiple independent players on one page.
- **Playback errors are events, API misuse throws.** Runtime/media errors use `DashJSError` + `EventBus` (`Events.ERROR`). Calling `MediaPlayer` methods before `initialize()`/`attachSource()` or with bad arguments throws synchronously. Codes in `src/core/errors/Errors.js`.
- **Protection/DRM is opt-in.** Call `player.setProtectionData()` explicitly.
- **`player.extend()` must be called BEFORE `initialize()`.**

### Code changes
- **PRs target `development`**, not `main`/`master`.
- **BSD-3-Clause header required** in every new source file.
- **v5 API — don't use deprecated v4 methods:**
  - `getBitrateInfoListFor()` → `getRepresentationsByType(type)`
  - `setQualityFor()` → `setRepresentationForTypeByIndex(type, index, forceReplace)`
  - `getQualityFor()` → `getCurrentRepresentationForType(type)`
- **New settings** need both `Settings.js` (value + JSDoc) and `index.d.ts`.
- **New samples** must update `samples/samples.json`.

## Where to look

| What | Where |
|---|---|
| Build scripts | `package.json` → `scripts` |
| Lint rules | `eslint.config.mjs` + `.editorconfig` |
| Architecture pattern | Any `src/` file — look for `FactoryMaker` |
| Test patterns | Any file in `test/unit/test/` |
| Test naming | `test/unit/test/` mirrors `src/` with dot-separated paths: `core.EventBus.js` → `src/core/EventBus.js` |
| Mocks | `test/unit/mocks/` |
| Test fixtures | `test/unit/data/` |
| API surface | `src/streaming/MediaPlayer.js` |
| Public exports | `index.js` + `index_mediaplayerOnly.js` |
| TypeScript defs | `index.d.ts` |
| Webpack entries | `build/webpack/common/webpack.common.base.cjs` |
| Sample registry | `samples/samples.json` |
| CI pipelines | `.github/workflows/` |