Polyfill DOMException

[davidliu]

Fixes #337 and livekit/client-sdk-js#1871.

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[florianpreusner]

Hi @davidliu — quick heads-up: we tested 2.10.1 in an Expo SDK 55 / Hermes app and the original Property 'DOMException' doesn't exist crash from #337 still reproduces. After tracing it, I think this PR's polyfill is wired in one line too late in src/index.tsx. Sharing the diagnosis in case it helps.

Setup

• @livekit/react-native@2.10.1, @livekit/react-native-webrtc@144.0.0, livekit-client@2.18.6
• Expo SDK 55, Hermes, iOS dev client (Android also affected)
• Metro resolves @livekit/react-native via the package's exports.default → lib/commonjs/index.js

Trace (before fix)

Instrumented console.log at the top of each side-effect-import file in lib/commonjs/ plus livekit-client.umd.js:

[DIAG] MediaRecorderShim    eval; global.DOMException = undefined
[DIAG] livekit-client.umd   eval; global.DOMException = undefined   ← would throw here
[DIAG] DOMException polyfill eval; global.DOMException = undefined  ← never reached in time

MediaRecorderShim is required on line 47 of compiled index.js, before the DOMException polyfill on line 48 (mirroring src/index.tsx lines 3-4). Its transitive chain is:

./polyfills/MediaRecorderShim
  → ../audio/MediaRecorder
    → ../logger              ← does `import { … } from 'livekit-client'`
      → livekit-client       ← top-level `class DeferrableMapAbortError extends DOMException`

So livekit-client evaluates during the require of line 3, before line 4 (the polyfill import) ever runs. The direct livekit-client imports lower in index.tsx (useParticipant, useRoom, LiveKitRoom, etc.) are fine because by the time those re-exports load, the polyfill has run — the issue is the indirect chain through MediaRecorderShim → MediaRecorder → logger.

Verified fix — swap lines 3 and 4

 import 'well-known-symbols/Symbol.asyncIterator/auto';
 import 'well-known-symbols/Symbol.iterator/auto';
-import './polyfills/MediaRecorderShim';
 import './polyfills/DOMException';
+import './polyfills/MediaRecorderShim';

After the swap, the same trace becomes:

[DIAG] DOMException polyfill eval; global.DOMException = undefined → installs polyfill
[DIAG] MediaRecorderShim    eval; global.DOMException = function
[DIAG] livekit-client.umd   eval; global.DOMException = function    ← happy

App boots cleanly, no consumer-side polyfill needed.

Happy to open a PR if helpful — just wanted to flag this since #337 is closed and other users on 2.10.1 will hit the same crash.