Can a library make sure Webpack removes a branch depending on whether React version is >= 18?

[alexeyr-ci2]

Currently we have

https://github.com/shakacode/react_on_rails/blob/74dc30bfedba28b7d171710e6d01066cad11eb89/node_package/src/reactApis.ts#L3-L8:

const reactMajorVersion = Number(ReactDOM.version?.split('.')[0]) || 16;

export const supportsRootApi = reactMajorVersion >= 18;

and use it as https://github.com/shakacode/react_on_rails/blob/74dc30bfedba28b7d171710e6d01066cad11eb89/node_package/src/reactHydrateOrRender.ts#L10-L30:

let reactDomClient: typeof import('react-dom/client');
if (supportsRootApi) {
  // This will never throw an exception, but it's the way to tell Webpack the dependency is optional
  // https://github.com/webpack/webpack/issues/339#issuecomment-47739112
  // Unfortunately, it only converts the error to a warning.
  try {
    // eslint-disable-next-line global-require,@typescript-eslint/no-require-imports
    reactDomClient = require('react-dom/client') as typeof import('react-dom/client');
  } catch (_e) {
    // We should never get here, but if we do, we'll just use the default ReactDOM
    // and live with the warning.
    reactDomClient = ReactDOM as unknown as typeof import('react-dom/client');
  }
}

const reactHydrate: HydrateOrRenderType = supportsRootApi
  ? reactDomClient!.hydrateRoot
  : (domNode, reactElement) => ReactDOM.hydrate(reactElement, domNode);

Is there any way for the library to be modified so Webpack automatically leaves only the correct branch depending on the React version in the bundle, without the clients needing to modify their Webpack config?

Failing that, should we just recommend using WebpackDefinePlugin to make supportsRootApi a constant, so Terser (or another minifier) can eliminate the unused branch?

[alexander-akait]

Failing that, should we just recommend using WebpackDefinePlugin to make supportsRootApi a constant, so Terser (or another minifier) can eliminate the unused branch?

Yes, it is a valid solution, alternative you can write custom babel/swc plugin and remove set something to true/false