Proxy pattern

Proxy Pattern nima?

Proxy Pattern — bu structural design pattern bo‘lib, u boshqa bir target object bilan o‘zaro ishlashni nazorat qilish uchun proxy yaratadi. JavaScriptda bu pattern uchun, Proxy API ni ishlatsak bo’ladi.

Proxy orqali biz object bilan bo‘layotgan har bir interaction ni (masalan, property ni o‘qish, yozish, method chaqirish) ushlab qolishimiz va o‘zimiz xohlagan behavior ni qo‘shishimiz mumkin.

Proxy Pattern quyidagi holatlarda juda foydali:

Access control — object ga kirishni cheklash
Validation — object ga berilayotgan qiymatlarni tekshirish
Logging — qaysi property o‘qildi yoki o‘zgartirildi
Lazy initialization — object ni faqat kerak bo‘lganda yaratish
Caching — qayta-qayta hisoblanadigan qiymatlarni saqlash

JavaScript dagi Proxy object

JavaScriptda Proxy global constructor bo‘lib, u ikki argument qabul qiladi:

const proxy = new Proxy(target, handler);

target — asl object
handler — (interception logic) bu ma’lum bir operationni ushlab qoluvchi function (masalan get, set).

Quyidagi misolda biz proxy orqali, object dan property o’qish jarayoniga o’zimizning logikamizi qo’shamiz:

const user = {
  name: "Alp Er To'nga",
  age: 25,
};

const userProxy = new Proxy(user, {
  get(target, property) {
    console.log(`Accessing property: ${property}`);
    return target[property];
  },
});

console.log(userProxy.name);
// Accessing property: name
// Alp Er To'nga

Yuqoridagi misolda objectning get qilish jarayoniga o’zimizning funksiyamizi qo’shgan bo’lsak, quyida set qilish jarayoniga validation qo’shib ko’ramiz:

const userProxy = new Proxy(user, {
  set(target, property, value) {
    if (property === "age" && value < 0) {
      throw new Error("Age cannot be negative");
    }

    target[property] = value;
    return true;
  },
});

userProxy.age = 30; // OK
userProxy.age = -5; // Error

Access control (himoyalangan property)

const user = {
  username: "admin",
  password: "secret",
};

const secureUser = new Proxy(user, {
  get(target, property) {
    if (property === "password") {
      throw new Error("Access denied");
    }

    return target[property];
  },
});

console.log(secureUser.username);
console.log(secureUser.password); // Error - Access denied