The React module does not support Yarn >v1.

[quisido]

I'm using Yarn 4.6, and posthog-js fails because react is not declared as a peer dependency (or dependency).

Here's the error as it comes from GitHub Actions CI:

Error: posthog-js tried to access react, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.%0A%0ARequired package: react%0ARequired by: posthog-js@npm:1.214.0 (via /home/runner/.yarn/berry/cache/posthog-js-npm-1.214.0-b6fee74acf-10c0.zip/node_modules/posthog-js/react/dist/umd/)%0A%0ARequire stack:%0A- /home/runner/.yarn/berry/cache/posthog-js-npm-1.214.0-b6fee74acf-10c0.zip/node_modules/posthog-js/react/dist/umd/index.js%0A ❯ Function.require$$0.Module._resolveFilename ../../.pnp.cjs:34662:13%0A ❯ Function.require$$0.Module._load ../../.pnp.cjs:34553:31%0A ❯ ../../../../../.yarn/berry/cache/posthog-js-npm-1.214.0-b6fee74acf-10c0.zip/node_modules/posthog-js/react/dist/umd/index.js:2:108%0A%0A⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯%0ASerialized Error: { code: 'MODULE_NOT_FOUND', pnpCode: 'UNDECLARED_DEPENDENCY', data: { request: 'react', issuer: '/home/runner/.yarn/berry/cache/posthog-js-npm-1.214.0-b6fee74acf-10c0.zip/node_modules/posthog-js/react/dist/umd/', issuerLocator: { name: 'posthog-js', reference: 'npm:1.214.0' }, dependencyName: 'react' }, requireStack: [ '/home/runner/.yarn/berry/cache/posthog-js-npm-1.214.0-b6fee74acf-10c0.zip/node_modules/posthog-js/react/dist/umd/index.js' ] }%0A

You may be looking for peerDependenciesMeta, since you are vending multiple library integrations in a single package: https://stackoverflow.com/questions/62047806/how-do-i-set-a-peer-dependency-optional