Add TypeScript declaration for the performance global

Description

Hey! React Native installs a performance global on every app, but its TypeScript types do not declare it.

Libraries/Core/setUpPerformance.js installs the global. It uses setUpPerformanceModern() when NativePerformance exists, and a fallback with only performance.now() otherwise.
src/private/webapis/performance/Performance.js is the implementation: now, timeOrigin, mark, measure, clearMarks, clearMeasures, getEntries, getEntriesByType, getEntriesByName, memory, eventCounts, rnStartupTiming.
src/types/globals.d.ts declares neither performance nor Performance. No other .d.ts in the package does.

This is the same gap as #56325 (TextEncoder / TextDecoder).

Happy to submit a PR if that helps

Steps to reproduce

tsconfig.json

{ "compilerOptions": { "lib": ["es2022"], "types": ["react-native"], "strict": true, "noEmit": true } }

.ts file

const start = performance.now();
const p: Performance = performance;

error

error TS2304: Cannot find name 'performance'.
error TS2304: Cannot find name 'Performance'.

React Native Version

0.85.3

Affected Platforms

Other (please specify)

Output of `npx @react-native-community/cli info`

this is just adding ts declarations

Stacktrace or Logs

this is just adding ts declarations

MANDATORY Reproducer

this is just adding ts declarations

Screenshots and Videos

No response

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I've also found that queueMicrotask is also missing TS declarations as well. See here

react-native/packages/react-native/Libraries/Core/Timers/queueMicrotask.js

Line 22 in 53237c7

export default function queueMicrotask(callback: () => unknown) {

We currently declare it ourself like this

declare global {
  function queueMicrotask(callback: () => void): void;
}

atob and btoa are also missing ts declarations. See here https://github.com/facebook/hermes/blob/6e2181b288b0306d8bd1988d38d32aa879b745d5/lib/VM/JSLib/GlobalObject.cpp#L768-L771

We currently declare it ourself like this

declare global {
  function atob(data: string): string;
  function btoa(data: string): string;
}

@johnnycheng0210

Thanks for the detailed write-up @johnnycheng0210! Since there hadn't been activity for a couple of weeks, I opened #58831, which adds declarations for performance / Performance / PerformanceEntry / PerformanceMark / PerformanceMeasure along with type tests. Sorry if you were already working on it, and your review there would be very welcome.

I kept that PR scoped to performance. The queueMicrotask, atob and btoa gaps you mentioned aren't covered yet, so they're still open for a follow-up.

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Add TypeScript declaration for the performance global #58610

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Output of `npx @react-native-community/cli info`

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Add TypeScript declaration for the performance global #58610

Description

Description

Steps to reproduce

React Native Version

Affected Platforms

Output of npx @react-native-community/cli info

Stacktrace or Logs

MANDATORY Reproducer

Screenshots and Videos

Activity

react-native-bot commented on Sep 21, 2026

johnnycheng0210 commented on Oct 1, 2026

johnnycheng0210 commented on Oct 1, 2026

Cedric921 commented on Oct 4, 2026

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Output of `npx @react-native-community/cli info`