Module Internals — Series 3

Preview — 3 of 10 questions

Both call sites pass what looks like identical configuration, yet two module instances appear. Why?

javascript

SharedModule.forRoot({ retries: 3, onError: (err) => logger.error(err) })
// imported from two different modules with the same literal

ABecause forRoot() deliberately creates a fresh instance per importer

BBecause the module was not marked @Global()

CBecause the token is derived from the module class plus a serialisation of the dynamic metadata, and a function value cannot be serialised into a stable, comparable form — two structurally "identical" literals produce different tokens, so the cache misses and the module is registered twice

DBecause object literals are compared by reference, so no two calls ever match

Why are modules discovered before their dependencies are read?

javascript

DependenciesScanner: scanForModules(...)  →  scanModulesForDependencies(...)

ABecause every module must exist in the container before relationships are resolved — imports, exports and providers all reference modules and tokens that may be declared later in the traversal, so a single pass would hit references to modules not yet registered

BBecause the first pass validates decorators and the second compiles TypeScript metadata

CBecause controllers are registered in the first pass and providers in the second

DBecause the first pass runs synchronously and the second asynchronously

A provider in a module importing CoreModule injects LoggerService. How is it found?

javascript

@Module({ providers: [LoggerService], exports: [LoggerService] })
export class LoggerModule {}

@Module({ imports: [LoggerModule], exports: [LoggerModule] })
export class CoreModule {}

ACoreModule is required to re-declare LoggerService in its own providers for this to work

BThe container flattens all exports into one global registry at startup

CThe token is resolved by scanning every module in the container until a match is found

DExporting a module rather than a token means "everything this module exports is also exported by me", so resolution follows the export chain: the importer looks in CoreModule's exports, finds LoggerModule listed, and continues into that module's own exports

Answer all 10 questions (7 more), see explanations for every answer, and track your score.