State

• Object behaves differently based on its state
• One base class and multiple children that implement and modify the state

interface State {
  think(): string;
}

class HappyState implements State {
  think() {
    return "I am happy 🙂";
  }
}

class SadState implements State {
  think() {
    return "I am sad 🙁";
  }
}

class Human {
  state: State;

  constructor() {
    this.state = new HappyState();
  }

  changeState(state) {
    this.state = state;
  }

  think() {
    return this.state.think();
  }
}

const human = new Human();
console.log(human.think());
human.changeState(new SadState());
console.log(human.think());