备忘录模式#

// 以文本编辑器为例，该编辑器会不时地保存状态，并且可以根据需要进行恢复。

class EditorMemento { // memento对象将能够保持编辑器状态
    constructor(content) {
        this._content = content;
    }
    
    getContent() {
        return this._content;
    }
}

class Editor {
    constructor(){
        this._content = "";
    }
    
    type(words) {
        this._content = `${this._content} ${words}`;
    }
    
    getContent() {
        return this._content;
    }
    
    save() {
        return new EditorMemento(this._content);
    }
    
    restore(memento) {
        this._content = memento.getContent();
    }
}

(function(){
    const editor = new Editor()

    editor.type("This is the first sentence.");
    editor.type("This is second.");

    const saved = editor.save();

    editor.type("And this is third.")

    console.log(editor.getContent()); // This is the first sentence. This is second. And this is third.

    editor.restore(saved);

    console.log(editor.getContent()); // This is the first sentence. This is second.
})();