src/composite/index.ts

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

namespace CompositePattern {
  interface Component {
    operation(): void;
  }

  class Composite implements Component {
    private list: Component[];
    private s: String;

    constructor(s: String) {
      this.list = [];
      this.s = s;
    }

    public operation(): void {
      console.log("`operation of `", this.s);
      for (var i = 0; i < this.list.length; i += 1) {
        this.list[i].operation();
      }
    }

    public add(c: Component): void {
      this.list.push(c);
    }

    public remove(i: number): void {
      if (this.list.length <= i) {
        throw new Error("index out of bound!");
      }
      this.list.splice(i, 1);
    }
  }

  class Leaf implements Component {
    private s: String;
    constructor(s: String) {
      this.s = s;
    }
    public operation(): void {
      console.log("`operation` of Leaf", this.s, " is called.");
    }
  }

  // Client code

  var leaf1 = new Leaf("1"),
    leaf2 = new Leaf("2"),
    leaf3 = new Leaf("3"),
    composite1 = new Composite("Comp1"),
    composite2 = new Composite("Comp2");

  composite1.add(leaf1);
  composite1.add(leaf2);
  composite1.add(leaf3);

  composite1.remove(2);

  composite2.add(leaf1);
  composite2.add(leaf3);

  composite1.operation();
  composite2.operation();

  console.log("composite1 + composite2");

  composite1.add(composite2);
  composite1.operation();

  // Output

  /*
    `operation of ` Comp1
    `operation` of Leaf 1  is called.
    `operation` of Leaf 2  is called.
    `operation of ` Comp2
    `operation` of Leaf 1  is called.
    `operation` of Leaf 3  is called.
    composite1 + composite2
    `operation of ` Comp1
    `operation` of Leaf 1  is called.
    `operation` of Leaf 2  is called.
    `operation of ` Comp2
    `operation` of Leaf 1  is called.
    `operation` of Leaf 3  is called.
  */
}