アクセサプロパティの定義 | getterとsetter | JavaScript 超完全入門 基本から発展までのすべて

const person = {
    firstName: "Taro",
    lastName: "Yamada",
    get fullName() {
        return this.firstName + " " + this.lastName;
    },
    set fullName(name) {
        const parts = name.split(" ");
        this.firstName = parts[0];
        this.lastName = parts[1];
    }
};

console.log(person.fullName);  // "Taro Yamada"

person.fullName = "Hanako Suzuki";
console.log(person.firstName);  // "Hanako"
console.log(person.lastName);   // "Suzuki"

const user = {
    ageValue: 25,
    get age() {
        return this.ageValue + "歳";
    },
    set age(value) {
        if (value > 0) {
            this.ageValue = value;
        }
    }
};

console.log(user.age);  // "25歳"
user.age = 30;
console.log(user.age);  // "30歳"

const account = {
    _balance: 1000,
    get balance() {
        return "現在の残高は " + this._balance + " 円です";
    },
    set balance(amount) {
        if (amount >= 0) {
            this._balance = amount;
        } else {
            console.log("無効な値です");
        }
    }
};

console.log(account.balance);  // "現在の残高は 1000 円です"
account.balance = -500;        // "無効な値です"
console.log(account.balance);  // "現在の残高は 1000 円です"