JavaScript Design Patterns - Behavioral - State

The state pattern allows an object to alter its behavior when its internal state changes.

In this example, we create a simple state pattern with an Order class that will update the status with the next() method.

const ORDER_STATUS = {
  waitingForPayment: 'Waiting for payment',
  shipping: 'Shipping',
  delivered: 'Delivered',
};

class OrderStatus {
  constructor(name, nextStatus) {
    this.name = name;
    this.nextStatus = nextStatus;
  }

  next() {
    return new this.nextStatus();
  }
}

class WaitingForPayment extends OrderStatus {
  constructor() {
    super(ORDER_STATUS.waitingForPayment, Shipping);
  }
}

class Shipping extends OrderStatus {
  constructor() {
    super(ORDER_STATUS.shipping, Delivered);
  }
}

class Delivered extends OrderStatus {
  constructor() {
    super(ORDER_STATUS.delivered, Delivered);
  }
}

class Order {
  constructor() {
    this.state = new WaitingForPayment();
  }

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

export { Order };

A complete example is here 👉 https://stackblitz.com/edit/vitejs-vite-6zcfql?file=state.js

Conclusion

Use this pattern when the object’s behavior depends on its state, and its behavior changes in runtime depending on that state.

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