Piye cara prototypal inheritance bisa berfungsi?

Question

IT Interview Practice · Accepted Answer

Saben JavaScript object duwe hubungan tersembunyi menyang object liyane sing diarani **prototype**. Saat sampeyan ngakses property, JS nggoleki ing object dhewe, banjur mlaku munggah ing **prototype chain** nganti nemokne property utawa nggawe `null`. Iki isih *delegation*, dudu ngubengi.

```js
const animal = {
  speak() { return `${this.name} makes a sound`; },
};

const dog = Object.create(animal); // dog's prototype IS animal
dog.name = "Rex";
dog.speak();                       // "Rex makes a sound" — found on the prototype

Object.getPrototypeOf(dog) === animal; // true
dog.hasOwnProperty("speak");           // false — it's inherited, not own
dog.hasOwnProperty("name");            // true
```

## Piye classes nggunakne

`class` adalah syntax sugar menyang prototypes. Methods manggon **sesowan** ing prototype, dibagi dening kabeh instances (ora dicopya per object):

```js
class Dog {
  constructor(name) { this.name = name; }
  speak() { return `${this.name} barks`; } // on Dog.prototype
}
const d = new Dog("Rex");
Object.getPrototypeOf(d) === Dog.prototype; // true
```

Dadi `d.speak` ora nyimpen ing `d` — iku ditemokne dening mlaku munggah menyang `Dog.prototype`. Kuwi sebab kabeh dog ibagi siji function `speak` (hemat memori).

## Apa gunane

Pangertosan chain njelasne: kenapa instances ibagi methods, kenapa owah-owahan prototype nagaruhi kabeh linked objects, piye `instanceof` bisa berfungsi (iku ngecheck chain), lan biaya ring lookup chains sing dawa.

Iku fondasi ing jero `class`, built-ins (`Array.prototype.map`), lan inheritance.

Piye classes nggunakne

Apa gunane

Pitakon sing gegandhengan