Dynamic import produces duplicate class instance in production

Don't use import(import.meta.url) as a singleton mechanism. In Vite dev this may appear to work because modules are served close to native ESM semantics, but production builds are builds are bundled and chunked. The module URL you see in source is not a stable identity boundary after build.

Move the singleton/state to a separate module and import that module from both places. If you need lazy loading, keep a cached promise using a static import specifier. If your app can load multiple bundles that each contain X, then module-singleton semanticas are not enough; use an explicit shared registry, dependency injection, or externalize X so there is only one physical copy.

Example:

// x-loader.ts let xPromise: Promise<typeof import('./x')> | undefined export function loadX() { return (xPromise ??= import('./x')) }

and if what you actually need is shared state:

// x-singleton.ts export const xSingleton = createX() // anywhere import { xSingleton } from './x-singleton'

Make module identity boring. Do not make correctness depend on how Vite decides to chunk production output.