# Optional

**Kind:** Function

**Source:** [`packages/common/decorators/core/optional.decorator.ts`](https://github.com/nestjs/nest/blob/master/packages/common/decorators/core/optional.decorator.ts#L20)

**Part of:** [Common](subsystem-packages-common)

Parameter decorator for an injected dependency marking the
dependency as optional.

For example:
```typescript
constructor(@Optional()

`Optional()` is a parameter decorator that marks a constructor dependency as optional in Nest's dependency injection system. If the requested provider is not available, Nest injects `undefined` instead of throwing a resolution error, allowing the consuming class to handle the absence of that dependency.

## Signature

```ts
function Optional(): PropertyDecorator & ParameterDecorator
```

**Returns:** `PropertyDecorator & ParameterDecorator`

## Diagram

```mermaid
graph LR
  A[Constructor parameter] --> B["@Optional()"]
  B --> C[Nest dependency injector]
  C -->|Provider available| D[Inject provider instance]
  C -->|Provider unavailable| E[Inject undefined]
  D --> F[Consumer handles dependency]
  E --> F
```

## Usage

```typescript
import { Inject, Injectable, Optional } from '@nestjs/common';

@Injectable()
export class AuditService {
  constructor(
    @Optional()
    @Inject('AUDIT_LOGGER')
    private readonly logger?: { log(message: string): void },
  ) {}

  recordEvent(event: string) {
    this.logger?.log(`Audit event: ${event}`);
  }
}
```

## AI Coding Instructions

- Use `@Optional()` only on constructor parameters managed by Nest's dependency injection container.
- Combine it with `@Inject()` when injecting optional custom tokens, interfaces, or string/symbol-based providers.
- Type optional dependencies as optional (`dependency?: Type`) or explicitly handle `undefined` before using them.
- Do not use `@Optional()` to hide required configuration or provider-registration mistakes; use it only when the dependency is genuinely optional.
- Ensure consumers safely degrade when the provider is absent, for example with optional chaining or a fallback implementation.

## Used by

8 references from 8 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (8)

- `DefaultsService` — `integration/injector/src/defaults/defaults.service.ts`:4
- `DefaultsService` — `integration/inspector/src/defaults/defaults.service.ts`:4
- `AnyFilesInterceptor` — `packages/platform-express/multer/interceptors/any-files.interceptor.ts`:24
- `FileFieldsInterceptor` — `packages/platform-express/multer/interceptors/file-fields.interceptor.ts`:27
- `FileInterceptor` — `packages/platform-express/multer/interceptors/file.interceptor.ts`:25
- `FilesInterceptor` — `packages/platform-express/multer/interceptors/files.interceptor.ts`:27
- `NoFilesInterceptor` — `packages/platform-express/multer/interceptors/no-files.interceptor.ts`:24
- `BaseExceptionFilter` — `packages/core/exceptions/base-exception-filter.ts`:17