Facade

Provides a single, simplified interface that hides the complexity of a subsystem. Clients use the facade instead of the many subsystem classes directly.

When to Use

• A subsystem has many classes with complex interactions
• You want to layer your architecture (facade = entry point to a layer)
• Integration with a complex library or framework should be encapsulated
• You need a simple default use case while keeping the subsystem accessible for advanced use

How to Apply

1. Check whether a simpler interface is possible and valuable
2. Declare and implement the Facade class, delegating to subsystem classes
3. Clients call the facade instead of directly accessing subsystem classes
4. Keep subsystem classes accessible for clients that need fine-grained control

Example

// Complex subsystem
class VideoDecoder  { decode(file: string)  { /* … */ } }
class AudioMixer    { fix(audio: string)    { /* … */ } }
class BitrateReader { read(file: string)    { return 1080; } }

// Facade
class VideoConverter {
  private decoder = new VideoDecoder();
  private mixer   = new AudioMixer();
  private reader  = new BitrateReader();

  convert(filename: string, format: string): string {
    const bitrate = this.reader.read(filename);
    this.decoder.decode(filename);
    this.mixer.fix(filename);
    return `output.${format}`;
  }
}

// Client only needs one call
const converter = new VideoConverter();
const output = converter.convert('funny-cats.ogg', 'mp4');

References

• refactoring.guru/design-patterns/facade