Function Inject

packages/common/decorators/core/inject.decorator.ts:38–68

(
  token?: InjectionToken | ForwardReference,
)

 * @publicApi
 */
export function Inject(
  token?: InjectionToken | ForwardReference,
): PropertyDecorator & ParameterDecorator {
  const injectCallHasArguments = arguments.length > 0;

  return (target: object, key: string | symbol | undefined, index?: number) => {
    let type = token || Reflect.getMetadata('design:type', target, key!);
    // Try to infer the token in a constructor-based injection
    if (!type && !injectCallHasArguments) {
      type = Reflect.getMetadata(PARAMTYPES_METADATA, target, key!)?.[index!];
    }

    if (!isUndefined(index)) {
      let dependencies =
        Reflect.getMetadata(SELF_DECLARED_DEPS_METADATA, target) || [];

      dependencies = [...dependencies, { index, param: type }];
      Reflect.defineMetadata(SELF_DECLARED_DEPS_METADATA, dependencies, target);
      return;
    }
    let properties =
      Reflect.getMetadata(PROPERTY_DEPS_METADATA, target.constructor) || [];

    properties = [...properties, { key, type }];
    Reflect.defineMetadata(
      PROPERTY_DEPS_METADATA,
      properties,
      target.constructor,
    );
  };
}