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State

Object Behavioural Design Pattern.

Example

interface ATMState { name?: string; takeCash(cash: number): void; } class ATMHasCashState implements ATMState { private _machine: ATMMachine; name: string; constructor(machine: ATMMachine, name: string) { this.name = name; this._machine = machine; } takeCash(cash: number): void { if (this._machine.cash < cash) { this._machine.state = this._machine.noCashState(); console.log('Not enough cash'); return; } else if (this._machine.cash === cash) { this._machine.state = this._machine.noCashState(); console.log('No cash after cash token'); } console.log( `[current machine total - cash]: ${this._machine.cash} - ${cash}` ); this._machine.cash -= cash; } } class ATMNoCashState implements ATMState { private _machine: ATMMachine; name: string; constructor(machine: ATMMachine, name: string) { this.name = name; this._machine = machine; } takeCash(cash: number): void { throw new Error('ATMMachine has no cash'); } } class ATMMachine implements ATMState { private _hasCashState: ATMHasCashState; private _noCashState: ATMNoCashState; private _currentState: ATMState; public cash: number; constructor(cash: number) { this.cash = cash; this._hasCashState = new ATMHasCashState(this, 'HasCash'); this._noCashState = new ATMNoCashState(this, 'NoCash'); this._currentState = this.cash ? this._hasCashState : this._noCashState; } public set state(value: ATMState) { console.log(`Current state is ${value.name}`); this._currentState = value; } public get state() { return this._currentState; } takeCash(cash: number): void { this._currentState.takeCash(cash); } // Get states public hasCashState() { return this._hasCashState; } public noCashState() { return this._noCashState; } } (function main() { const machine = new ATMMachine(1200); machine.takeCash(200); // has cash machine.takeCash(400); // has cash machine.takeCash(1000); // not enough })();

Repository

https://github.com/okeeffed/developer-notes-nextjs/content/design-patterns/state

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