0x14 State

Review

  1. 2024-09-17 16:43

[!Summary]

一、Introduction #

The state pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. This pattern is useful when you have an object that can exist in multiple states, and the behavior of the object should change depending on its current state.

interface State {
  handle(context: Context): void;
}

class ConcreteStateA implements State {
  handle(context: Context): void {
    console.log("State A");
    context.setState(new ConcreteStateB());
  }
}

class ConcreteStateB implements State {
  handle(context: Context): void {
    console.log("State B");
    context.setState(new ConcreteStateA());
  }
}

class Context {
  private state: State;

  constructor(state: State) {
    this.state = state;
  }

  request(): void {
    this.state.handle(this);
  }

  setState(state: State): void {
    this.state = state;
  }
}

// Client code
const context = new Context(new ConcreteStateA());
context.request();
context.request();
context.request();

Reference #