TypeScript 备忘录模式讲解和代码示例

/** * The Originator holds some important state that may change over time. It also * defines a method for saving the state inside a memento and another method for * restoring the state from it. */ class Originator { /** * For the sake of simplicity, the originator's state is stored inside a * single variable. */ private state: string; constructor(state: string) { this.state = state; console.log(`Originator: My initial state is: ${state}`); } /** * The Originator's business logic may affect its internal state. Therefore, * the client should backup the state before launching methods of the * business logic via the save() method. */ public doSomething(): void { console.log('Originator: I\'m doing something important.'); this.state = this.generateRandomString(30); console.log(`Originator: and my state has changed to: ${this.state}`); } private generateRandomString(length: number = 10): string { const charSet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; return Array .apply(null, { length }) .map(() => charSet.charAt(Math.floor(Math.random() * charSet.length))) .join(''); } /** * Saves the current state inside a memento. */ public save(): Memento { return new ConcreteMemento(this.state); } /** * Restores the Originator's state from a memento object. */ public restore(memento: Memento): void { this.state = memento.getState(); console.log(`Originator: My state has changed to: ${this.state}`); } } /** * The Memento interface provides a way to retrieve the memento's metadata, such * as creation date or name. However, it doesn't expose the Originator's state. */ interface Memento { getState(): string; getName(): string; getDate(): string; } /** * The Concrete Memento contains the infrastructure for storing the Originator's * state. */ class ConcreteMemento implements Memento { private state: string; private date: string; constructor(state: string) { this.state = state; this.date = new Date().toISOString().slice(0, 19).replace('T', ' '); } /** * The Originator uses this method when restoring its state. */ public getState(): string { return this.state; } /** * The rest of the methods are used by the Caretaker to display metadata. */ public getName(): string { return `${this.date} / (${this.state.substr(0, 9)}...)`; } public getDate(): string { return this.date; } } /** * The Caretaker doesn't depend on the Concrete Memento class. Therefore, it * doesn't have access to the originator's state, stored inside the memento. It * works with all mementos via the base Memento interface. */ class Caretaker { private mementos: Memento[] = []; private originator: Originator; constructor(originator: Originator) { this.originator = originator; } public backup(): void { console.log('\nCaretaker: Saving Originator\'s state...'); this.mementos.push(this.originator.save()); } public undo(): void { if (!this.mementos.length) { return; } const memento = this.mementos.pop(); console.log(`Caretaker: Restoring state to: ${memento.getName()}`); this.originator.restore(memento); } public showHistory(): void { console.log('Caretaker: Here\'s the list of mementos:'); for (const memento of this.mementos) { console.log(memento.getName()); } } } /** * Client code. */ const originator = new Originator('Super-duper-super-puper-super.'); const caretaker = new Caretaker(originator); caretaker.backup(); originator.doSomething(); caretaker.backup(); originator.doSomething(); caretaker.backup(); originator.doSomething(); console.log(''); caretaker.showHistory(); console.log('\nClient: Now, let\'s rollback!\n'); caretaker.undo(); console.log('\nClient: Once more!\n'); caretaker.undo(); 

Originator: My initial state is: Super-duper-super-puper-super. Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: qXqxgTcLSCeLYdcgElOghOFhPGfMxo Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: iaVCJVryJwWwbipieensfodeMSWvUY Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: oSUxsOCiZEnohBMQEjwnPWJLGnwGmy Caretaker: Here's the list of mementos: 2019-02-17 15:14:05 / (Super-dup...) 2019-02-17 15:14:05 / (qXqxgTcLS...) 2019-02-17 15:14:05 / (iaVCJVryJ...) Client: Now, let's rollback! Caretaker: Restoring state to: 2019-02-17 15:14:05 / (iaVCJVryJ...) Originator: My state has changed to: iaVCJVryJwWwbipieensfodeMSWvUY Client: Once more! Caretaker: Restoring state to: 2019-02-17 15:14:05 / (qXqxgTcLS...) Originator: My state has changed to: qXqxgTcLSCeLYdcgElOghOFhPGfMxo