src/flyweight/index.ts

// https://en.wikipedia.org/wiki/Flyweight_pattern

namespace FlyweightPattern {
  interface IFlyweight {
    code: number;
  }

  class Flyweight implements IFlyweight {
    code: number;
    constructor(code: number) {
      this.code = code;
    }
  }

  class FlyweightFactory {
    static flyweights: { [id: number]: Flyweight } = {};

    static getFlyweight(code: number): Flyweight {
      if (!(code in FlyweightFactory.flyweights)) {
        FlyweightFactory.flyweights[code] = new Flyweight(code);
      }
      return FlyweightFactory.flyweights[code];
    }

    static getCount(): number {
      return Object.keys(FlyweightFactory.flyweights).length;
    }
  }

  class AppContext {
    private codes: number[] = [];

    constructor(codes: string) {
      for (let i = 0; i < codes.length; i++) {
        this.codes.push(codes.charCodeAt(i));
      }
    }

    output() {
      let ret = "";
      this.codes.forEach((c) => {
        ret = ret + String.fromCharCode(FlyweightFactory.getFlyweight(c).code);
      });

      return ret;
    }
  }

  // Client code
  const context = new AppContext("abracadabra");
  console.log(context.output());
  console.log(`abracadabra has ${"abracadabra".length} letters`);
  console.log(`FlyweightFactory has ${FlyweightFactory.getCount()} flyweights`);

  // Output
  /*
  abracadabra
  abracadabra has 11 letters
  FlyweightFactory has 5 flyweights
  */
}