index.ts

class Context {
  private state: State

  constructor(state: State) {
    this.transitionTo(state)

  }

  public transitionTo(state: State): void {
    console.log(`Context: Transition to ${(<any>state).constructor.name}.`);
    this.state = state;
    this.state.setContext(this);
  }

  public request1(): void {
    this.state.handle1();
  }

  public request2(): void {
    this.state.handle2();
  }
}

abstract class State {
  protected context: Context

  public setContext(context: Context) {
    this.context = context
  }

  public abstract handle1(): void
  public abstract handle2(): void
}

class ConcreteStateA extends State {
  public handle1(): void {
    console.log('ConcreteStateA handles request1.');
    console.log('ConcreteStateA wants to change the state of the context.');
    this.context.transitionTo(new ConcreteStateB());
  }

  public handle2(): void {
    console.log('ConcreteStateA handles request2.');
  }
}

class ConcreteStateB extends State {
  public handle1(): void {
    console.log('ConcreteStateB handles request1.');
  }

  public handle2(): void {
    console.log('ConcreteStateB handles request2.');
    console.log('ConcreteStateB wants to change the state of the context.');
    this.context.transitionTo(new ConcreteStateA());
  }
}

function clientCodeContext() {
  const context = new Context(new ConcreteStateA());
  context.request1();
  context.request2();
}

export function state() {
  clientCodeContext()
}