Chapter 24 — Encapsulation, Getters/Setters

Bu bobda OOP'ning to'rtinchi asosiy ustuni — Encapsulationni, va uni Chapter 22'da ko'rgan Getter/Setter va Private Field'lar bilan qanday amalga oshirishni chuqur o'rganamiz.

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24.1 Encapsulation nima?

Simple Explanation

Encapsulation (inkapsulyatsiya) — ma'lumot (data) va uni boshqaruvchi metodlarni bitta joyda birlashtirish, hamda ma'lumotning ichki tuzilishini tashqi dunyodan "yashirish".

Why Does It Exist?

Agar object'ning barcha propertylari to'g'ridan-to'g'ri o'zgartirilaversa, dastur ichida nazoratsiz, noto'g'ri qiymatlar paydo bo'lishi mumkin. Encapsulation — ma'lumotni faqat "nazorat qilingan eshiklar" (metodlar) orqaligina o'zgartirishga majbur qiladi.

Real-Life Analogy

🚗 Mashina dvigatelini tasavvur qiling: haydovchi dvigatelning ichki mexanizmini bilishi shart emas va unga to'g'ridan-to'g'ri tegishi mumkin emas — u faqat "interfeys" (gaz pedali, rul) orqali mashinani boshqaradi. Dvigatelning o'zi — inkapsulyatsiya qilingan.

24.2 Nima uchun to'g'ridan-to'g'ri property'ga kirish xavfli?

Muammoli misol (Encapsulation'siz)

script.js
JavaScriptNusxalash
01class BankAccount {
02    constructor(balance) {
03        this.balance = balance;
04    }
05}
06 
07let account = new BankAccount(1000);
08 
09account.balance = -5000; // ❌ Hech qanday tekshiruvsiz, noto'g'ri qiymat!
10 
11console.log(account.balance); // -5000

Explanation

Bu yerda hech narsa balancening manfiy bo'lishining oldini olmayapti — chunki balance to'g'ridan-to'g'ri, hech qanday nazoratsiz o'zgartirilishi mumkin.

⚠️ Common Mistake
Barcha propertylarni ochiq (public) qilib qo'yish — kichik loyihalarda muammo tug'dirmasligi mumkin, lekin katta loyihalarda bu "har kim, har qanday joydan, har qanday noto'g'ri qiymat bilan ma'lumotni buzishi mumkin" degani.

24.3 Yechim — Private Field + Getter/Setter orqali Encapsulation

Example — to'g'ri yondashuv

script.js
JavaScriptNusxalash
01class BankAccount {
02    #balance;
03 
04    constructor(initialBalance) {
05        if (initialBalance < 0) {
06            throw new Error("Boshlang'ich balans manfiy bo'lishi mumkin emas");
07        }
08        this.#balance = initialBalance;
09    }
10 
11    get balance() {
12        return this.#balance;
13    }
14 
15    deposit(amount) {
16        if (amount <= 0) {
17            throw new Error("Depozit summasi musbat bo'lishi kerak");
18        }
19        this.#balance += amount;
20    }
21 
22    withdraw(amount) {
23        if (amount > this.#balance) {
24            throw new Error("Balansda yetarli mablag' yo'q");
25        }
26        this.#balance -= amount;
27    }
28}
29 
30let account = new BankAccount(1000);
31 
32account.deposit(500);
33console.log(account.balance); // 1500
34 
35account.withdraw(3000); // ❌ Error: Balansda yetarli mablag' yo'q

How It Works

1. #balance — private field, class tashqarisidan mutlaqo ko'rinmaydi va o'zgartirilmaydi.
2. get balance() — faqat o'qish uchun "eshik" ochadi (o'zgartirish uchun emas).
3. deposit(), withdraw() — #balanceni o'zgartirishning yagona yo'li, va ularning ichida tekshiruv (validation) mavjud.

Diagram

code.text
TEXTNusxalash
01Tashqi dunyo
02    │
03    ▼ (faqat metodlar orqali)
04┌─────────────────────┐
05│  BankAccount         │
06│                       │
07│  #balance (yashirin) │ ← to'g'ridan-to'g'ri kirib bo'lmaydi
08│                       │
09│  deposit()  ────┐    │
10│  withdraw() ─────┼──→│ #balance
11│  get balance() ──┘    │
12└─────────────────────┘

🔥 Important
Bu naqsh — Chapter 18'da o'rgangan Error Handling bilan Encapsulation'ning birgalikda ishlashiga aniq misol: noto'g'ri qiymat kiritilishga urinilganda, tizim buni jimgina qabul qilish o'rniga aniq xatolik bilan rad etadi.

24.4 ⚠️ Qiyin mavzu: "Convention-based" Private (eski usul)

Simple Explanation

# bilan private field'lar nisbatan yangi (ES2022). Undan oldin, dasturchilar "private"ni faqat kelishuv (convention) orqali — property nomi oldiga pastki chiziq (_) qo'yib — ifodalashgan.

Example

script.js
JavaScriptNusxalash
01class OldStyleAccount {
02    constructor(balance) {
03        this._balance = balance; // "men private bo'lishni xohlayman" degan ishora
04    }
05 
06    get balance() {
07        return this._balance;
08    }
09}
10 
11let acc = new OldStyleAccount(500);
12 
13console.log(acc._balance); // 500 — LEKIN bu ishlaydi!
14acc._balance = -1000;      // Bu ham "ishlaydi", garchi noto'g'ri bo'lsa ham

Nima uchun bu chin ma'noda private emas?

_balance — bu shunchaki oddiy property, faqat oldida _ bor. JavaScript uni haqiqiy private sifatida bloklamaydi — bu faqat boshqa dasturchilarga "bu propertyga tashqaridan tegmang" degan kelishuv (convention), lekin texnik jihatdan hech kim buni bloklamaydi.

Jadval — Solishtirish

💡 Key Idea
Zamonaviy loyihalarda har doim # ishlatish tavsiya etiladi — u haqiqiy xavfsizlikni ta'minlaydi, _ esa faqat "yaxshi niyat"ga tayanadi.

24.5 Getter/Setter orqali "Hisoblangan" (Computed) propertylar

Simple Explanation

Encapsulation faqat "himoya qilish" uchun emas, balki propertyni boshqa ma'lumotlar asosida dinamik hisoblash uchun ham ishlatiladi.

Example

script.js
JavaScriptNusxalash
01class Person {
02    constructor(firstName, lastName) {
03        this.firstName = firstName;
04        this.lastName = lastName;
05    }
06 
07    get fullName() {
08        return `${this.firstName} ${this.lastName}`;
09    }
10 
11    set fullName(value) {
12        let parts = value.split(" ");
13        this.firstName = parts[0];
14        this.lastName = parts[1];
15    }
16}
17 
18let person = new Person("Ali", "Valiyev");
19 
20console.log(person.fullName); // "Ali Valiyev"
21 
22person.fullName = "Vali Karimov";
23console.log(person.firstName); // "Vali"
24console.log(person.lastName);  // "Karimov"

Explanation

fullName — hech qayerda alohida saqlanmaydi, u har safar firstName va lastNamedan hisoblanadi (getter), va o'rnatilganda (setter) ularni avtomatik yangilaydi.

📝 Practice Exercises

🟢 Exercise 1 — Easy

Task:
#age (private field) bilan Person class yarating, get age() orqali uni o'qish imkonini bering, lekin tashqaridan to'g'ridan-to'g'ri o'zgartirib bo'lmasin.
Required Concepts:

• Private fields
• Getters
  Hint:
  Faqat get age() yozing, set age() yozmang — shunda u faqat o'qish uchun bo'ladi.

🟡 Exercise 2 — Medium

Task:
Temperature class yarating — #celsius private field bilan. get fahrenheit() getter qo'shing, u Celsius'ni Fahrenheitga aylantirib bersin (F = C * 9/5 + 32). set celsius(value) orqali faqat -273dan katta qiymatlar qabul qilinsin (aks holda xatolik).
Required Concepts:

• Private fields
• Getters/Setters
• Validation
  Hint:
  set celsius(value) { if (value < -273) throw new Error(...); this.#celsius = value; }

🔴 Exercise 3 — Hard

Task:
To'liq ShoppingCart class yarating: #items (private array). addItem(name, price), removeItem(name) metodlari, get total() getter (barcha narxlar yig'indisi), get itemCount() getter (mahsulotlar soni). Barcha metodlarga tegishli tekshiruvlar (validation) qo'shing.
Required Concepts:

• Private fields (array)
• Getters
• Array methods (Chapter 14-15)
  Hint:
  #items — object'lar array'i bo'lsin: { name, price }.

🔮 Predict the Output

script.js
JavaScriptNusxalash
01class Wallet {
02    #amount = 0;
03 
04    add(value) {
05        this.#amount += value;
06    }
07 
08    get amount() {
09        return this.#amount;
10    }
11}
12 
13let wallet = new Wallet();
14wallet.add(100);
15wallet.amount = 500; // to'g'ridan-to'g'ri o'zgartirishga urinish
16 
17console.log(wallet.amount);

🧠 Think first! Javobni ko'rishdan oldin kamida 30 soniya o'ylang.

<details> <summary>Answer</summary> 100

Why?
Wallet class'ida faqat get amount() bor, set amount() yo'q. Shuning uchun wallet.amount = 500 — jimgina e'tiborga olinmaydi (strict mode'da bo'lmasa xatolik ham bermaydi), chunki bu property faqat o'qish uchun (read-only). #amountning haqiqiy qiymati — faqat add() metodi orqali o'zgargan, u 100ga teng qolgan.

</details>

🐛 Debugging Challenge

Quyidagi kodda muammo bor:

script.js
JavaScriptNusxalash
01class User {
02    constructor(email) {
03        this.email = email;
04    }
05 
06    set email(value) {
07        if (!value.includes("@")) {
08            throw new Error("Email formati noto'g'ri");
09        }
10        this.email = value;
11    }
12}
13 
14let user = new User("test@example.com");

Your Task:

• Kod ishga tushganda nima bo'lishini bashorat qiling.
• Nima uchun bu infinite loop yaratishini tushuntiring (Chapter 22'dagi shunga o'xshash muammoni eslang).
• Kodni tuzating.

<details> <summary>Solution</summary> Muammo: set email(value) ichida this.email = value yozilgan — bu setterning o'zini qayta chaqiradi, chunki this.email = ... — bu setterni ishga tushiruvchi harakat. Natijada cheksiz rekursiya ("Maximum call stack size exceeded") yuzaga keladi.

Yechim: Ichki saqlash uchun boshqa nom (#_email yoki _email) ishlatish kerak:

script.js
JavaScriptNusxalash
01class User {
02    #email;
03 
04    constructor(email) {
05        this.email = email; // setterni chaqiradi
06    }
07 
08    set email(value) {
09        if (!value.includes("@")) {
10            throw new Error("Email formati noto'g'ri");
11        }
12        this.#email = value;
13    }
14 
15    get email() {
16        return this.#email;
17    }
18}
19 
20let user = new User("test@example.com");
21console.log(user.email); // "test@example.com"

</details>

📌 Chapter Summary

• Encapsulation — ma'lumotni yashirish va faqat nazorat qilingan metodlar orqali o'zgartirishga imkon berish.
• To'g'ridan-to'g'ri ochiq propertylar — nazoratsiz, xato qiymatlar xavfini tug'diradi.
• # bilan private field'lar — chinakam, texnik jihatdan himoyalangan yashirish.
• _ bilan boshlanuvchi nomlar — faqat kelishuv, haqiqiy himoya emas.
• Getter/Setter — validatsiya va hisoblangan propertylar uchun ishlatiladi.

🎯 Key Takeaways

• Zamonaviy kodda har doim # (private field) ishlating, _ emas.
• Setter ichida validatsiya qo'shish — noto'g'ri ma'lumotning oldini oladi.
• Faqat get yozib, set yozmaslik — propertyni "faqat o'qish uchun" qiladi.
• Getter/Setter nomi bilan ichki saqlash nomi bir xil bo'lmasligi kerak (infinite loop xavfi).
• Encapsulation — katta loyihalarda kodni ishonchli va xavfsiz qiladi.

⚡ Quick Cheat Sheet

script.js
JavaScriptNusxalash
01class Account {
02    #balance;
03 
04    constructor(balance) {
05        this.#balance = balance;
06    }
07 
08    get balance() {
09        return this.#balance;
10    }
11 
12    deposit(amount) {
13        if (amount <= 0) throw new Error("Noto'g'ri summa");
14        this.#balance += amount;
15    }
16}

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