When Angular modules use a static forRoot() function for configuration, importing them more than once can create multiple service instances, causing subtle and hard-to-debug bugs. This post explains the problem with singleton modules and presents two solutions using Angular's dependency injection system. The primary approach uses an InjectionToken combined with a factory function, Optional, and SkipSelf decorators to throw an error if forRoot() is called more than once. A simpler alternative injects the module into itself to detect duplicate imports, though it doesn't support forChild() usage. The post compares both approaches and references the Angular Router as a real-world example.
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An exampleShow me the codeThis can be prevented with 3 easy stepsA second solution but differentThe difference1 Impression