Optional class to default out variables when they do not exist.

optional.ts

class Optional<T> {

  private value: T | null = null;

  private constructor(value: T | null) {
    this.value = value;
  }

  public static some<T>(value: T): Optional<T> {
    return new Optional(value);
  }
  public static none<T>(): Optional<T> {
    return new Optional(null);
  }
  // helper method
  public static from<T>(value: T): Optional<T> {
    return value === null ? new Optional(null) : new Optional(value);
  }
  public getOr(alternative: T): T {
    return this.value ? this.value : alternative;
  }

}

Example usage with an imaginary IConfig interface:

class App {

  private config: IConfig;

  constructor(config: Optional<IConfig>) {
    this.config = config.getOr(new DefaultConfig());
  }

}