JavaScript meros (extends, super)

Bir necha klass umumiy xususiyatga ega bo’lsa, ularni har birida qayta yozish shart emas. Meros umumiy qismni bitta joyda saqlashga imkon beradi.

Muammo: takrorlanadigan klasslar

class Student {
  constructor(name, age) { this.name = name; this.age = age; }
  introduce() { return this.name + ", " + this.age + " age"; }
}

class Teacher {
  constructor(name, age) { this.name = name; this.age = age; }
  introduce() { return this.name + ", " + this.age + " age"; }
}

Ikkalasida ham name, age va introduce bir xil. Umumiy qismni ajratish kerak.

extends — kengaytirish

JavaScript

class Person {
constructor(name, age) {
  this.name = name;
  this.age = age;
}

introduce() {
  return this.name + ", " + this.age + " age";
}
}

class Student extends Person {
constructor(name, age, group) {
  super(name, age);
  this.group = group;
}
}

const aziz = new Student("Aziz", 20, "IT-21");

console.log(aziz.introduce());
console.log(aziz.group);

Student introduce metodini yozmagan, lekin u ishladi — ota klassdan meros qilib olindi.

super majburiy

Avlod constructor’ida this dan oldin super() chaqirilishi shart:

JavaScript

class Person {
constructor(name) {
  this.name = name;
}
}

class Student extends Person {
constructor(name, group) {
  try {
    this.group = group;
  } catch (error) {
    console.log("Xato:", error.message);
  }
  super(name);
  this.group = group;
}
}

const t = new Student("Aziz", "IT-21");
console.log(t.name, t.group);

Sababi: this obyekti ota constructor tomonidan yaratiladi — u chaqirilmaguncha this mavjud emas.

Metodni qayta yozish

Avlod ota metodini o’zinikiga almashtira oladi:

JavaScript

class Person {
constructor(name) {
  this.name = name;
}
introduce() {
  return "Men " + this.name;
}
}

class Teacher extends Person {
constructor(name, subject) {
  super(name);
  this.subject = subject;
}

introduce() {
  return super.introduce() + ", " + this.subject + " o'qituvchisi";
}
}

const person = new Person("Aziz");
const teacher = new Teacher("Dilnoza", "MathUtils");

console.log(person.introduce());
console.log(teacher.introduce());

super.tanishtir() ota versiyasini chaqirdi, so’ng natijaga qo’shimcha qo’shildi. Bu — noldan yozishdan ko’ra yaxshi usul.

Ko’p bosqichli meros

JavaScript

class Vehicle {
constructor(title) {
  this.title = title;
}
move() {
  return this.title + " harakatlanmoqda";
}
}

class Car extends Vehicle {
constructor(title, wheels) {
  super(title);
  this.wheels = wheels;
}
move() {
  return super.move() + " (" + this.wheels + " g'ildirak)";
}
}

class Truck extends Car {
constructor(title, wheels, capacity) {
  super(title, wheels);
  this.capacity = capacity;
}
move() {
  return super.move() + ", " + this.capacity + " tonna yuk bilan";
}
}

const y = new Truck("KamAZ", 6, 12);
console.log(y.move());

Zanjir bo’ylab har daraja o’z hissasini qo’shdi.

instanceof — turini tekshirish

JavaScript

class Person {}
class Student extends Person {}
class Teacher extends Person {}

const t = new Student();

console.log(t instanceof Student);
console.log(t instanceof Person);
console.log(t instanceof Teacher);

Obyekt butun zanjirga tegishli hisoblanadi: Student ham Person.

Amaliy misol — xato klasslari

Meros xatolarni turkumlashda ko’p ishlatiladi:

JavaScript

class AppError extends Error {
constructor(message, kod) {
  super(message);
  this.name = "AppError";
  this.kod = kod;
}
}

class NotFoundError extends AppError {
constructor(nima) {
  super(nima + " topilmadi", 404);
  this.name = "NotFoundError";
}
}

function find(title) {
if (title !== "Aziz") throw new NotFoundError("Student");
return { name: title };
}

try {
find("Kimdir");
} catch (error) {
console.log(error.name);
console.log(error.message);
console.log(error.kod);
console.log(error instanceof AppError);
console.log(error instanceof Error);
}

catch blokida instanceof bilan xato turiga qarab turlicha ish tutish mumkin.

Merosdan foydalanmaslik ham to’g’ri

Amaliy mashq

Animal klassini yozing: name va sound() metodi;
Dog va Cat klasslarini extends bilan yarating;
har birida sound() ni qayta yozing;
avlod constructor’iga qo’shimcha xossa qo’shing va super chaqiring;
super.ovoz() ni chaqirib, natijaga qo’shimcha qo’shing;
instanceof bilan uch xil tekshiruv o’tkazing.

Qisqacha xulosa

extends avlod klassni ota klass asosida yaratadi.
Avlod constructor’ida super() this dan oldin chaqirilishi shart.
Metod qayta yozilsa, ota versiyasi super.metod() bilan chaqiriladi.
instanceof butun meros zanjirini hisobga oladi.
Error dan meros olib, o’z xato turlaringizni yaratish mumkin.
Chuqur meros o’rniga ko’pincha kompozitsiya afzal.

Keyingi darsda Set va Map — maxsus to’plam turlari.