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GuidesIdentifier

Identifier

An identifier is a unique token used to look up a dependency from the injector.

Using a Class as Identifier

The simplest approach is to use the class itself as the identifier:

class AuthService {}
 
const injector = new Injector([[AuthService]]);
const auth = injector.get(AuthService);

This is convenient but couples your code to the concrete implementation.

For better abstraction, use createIdentifier to create an identifier for an interface:

// 1. Define the interface and create an identifier
interface IClipboardService {
  readText(): string | undefined;
}
 
const IClipboardService = createIdentifier<IClipboardService>("clipboard");

In TypeScript, type names and value names are in different namespaces. This allows us to use the same name IClipboardService for both the interface and the identifier.

// 2. Create different implementations
class WebClipboardService implements IClipboardService {
  readText() {
    return navigator.clipboard.readText();
  }
}
 
class MobileClipboardService implements IClipboardService {
  readText() {
    return bridge.readText();
  }
}
 
// 3. Inject different implementations based on environment
const injector = new Injector([
  [IClipboardService, { useClass: WebClipboardService }],  // for web
  // or
  [IClipboardService, { useClass: MobileClipboardService }], // for mobile
]);
 
// 4. Get the dependency - same code works in both environments
const clipboard = injector.get(IClipboardService);

Benefits of Using Identifiers

BenefitDescription
Loose couplingYour code depends on interfaces, not implementations
Easy testingSwap real services with mocks easily
FlexibilitySwitch implementations without changing consumer code
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