2nd/10_Wiki/Topic_JavaScript/JavaScript_Class_Inheritance.md

---
id: javascript-class-inheritance
title: "JavaScript Class Inheritance"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["extends", "super", "getters and setters", "class hoisting", "subclass"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.89
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools", "classes", "inheritance", "oop"]
raw_sources: ["https://www.w3schools.com/js/js_class_inheritance.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Class Inheritance]]

## 🎯 한 줄 통찰 (One-line insight)
Use `extends` to make one class inherit all methods of another and `super()` to reach the parent's constructor; classes also support `get`/`set` accessors and, unlike functions, are not hoisted. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`extends` for inheritance** — a class created with `extends` acquires all methods from another class. [S1]
- **`super()` references the parent** — calling `super()` in the constructor accesses parent properties and methods. [S1]
- **Inheritance aids reuse** — inheritance is useful for code reusability. [S1]
- **Getters and setters** — classes support `get` and `set` keywords for special property handling. [S1]
- **Getter access has no parentheses** — even though the getter is a method, you do not use parentheses to get the property value. [S1]
- **Classes are not hoisted** — unlike functions, classes must be declared before use. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Subclass = `extends` + `super(...)`** — pass parent constructor arguments through `super()`, then add subclass-specific state. [S1]
- **Underscore backing field for accessors** — store the value in `_carname` and expose it via `get carname()` / `set carname(x)` to avoid name collision with the accessor. [S1]
- **Declare before use** — because classes aren't hoisted, place the declaration ahead of any `new`. [S1]

## 📖 세부 내용 (Details)
**Class Inheritance**
To create class inheritance, use the `extends` keyword; the subclass acquires all methods of the parent. `super()` refers to the parent class, and calling it in the constructor accesses parent properties and methods. Inheritance is useful for code reusability: [S1]
```javascript
class Car {
  constructor(brand) {
    this.carname = brand;
  }
  present() {
    return 'I have a ' + this.carname;
  }
}

class Model extends Car {
  constructor(brand, mod) {
    super(brand);
    this.model = mod;
  }
  show() {
    return this.present() + ', it is a ' + this.model;
  }
}

let myCar = new Model("Ford", "Mustang");
document.getElementById("demo").innerHTML = myCar.show();
```

**Getters and Setters**
Classes support getters and setters using the `get` and `set` keywords: [S1]
```javascript
class Car {
  constructor(brand) {
    this.carname = brand;
  }
  get cnam() {
    return this.carname;
  }
  set cnam(x) {
    this.carname = x;
  }
}

const myCar = new Car("Ford");
document.getElementById("demo").innerHTML = myCar.cnam;
```
**Note:** Even if the getter is a method, you do not use parentheses when you want to get the property value. [S1]

Using an underscore backing field so the accessor name matches the property: [S1]
```javascript
class Car {
  constructor(brand) {
    this._carname = brand;
  }
  get carname() {
    return this._carname;
  }
  set carname(x) {
    this._carname = x;
  }
}

const myCar = new Car("Ford");
document.getElementById("demo").innerHTML = myCar.carname;
```
Using the setter to change the value: [S1]
```javascript
class Car {
  constructor(brand) {
    this._carname = brand;
  }
  get carname() {
    return this._carname;
  }
  set carname(x) {
    this._carname = x;
  }
}

const myCar = new Car("Ford");
myCar.carname = "Volvo";
document.getElementById("demo").innerHTML = myCar.carname;
```

**Hoisting**
Class declarations are not hoisted; classes must be declared before use: [S1]
```javascript
//You cannot use the class yet.
//myCar = new Car("Ford") will raise an error.

class Car {
  constructor(brand) {
    this.carname = brand;
  }
}

//Now you can use the class:
const myCar = new Car("Ford")
```
For other declarations, like functions, you will NOT get an error when you try to use it before it is declared, because the default behavior of JavaScript declarations is hoisting. [S1]

## 🛠️ 적용 사례 (Applied in summary)
The `Car` / `Model` pair is the running applied example for `extends` and `super()`; the `_carname` accessor examples demonstrate getters/setters, and the hoisting snippet shows the declare-before-use requirement. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Subclass with `extends` and `super()` (language: JavaScript):
```javascript
class Model extends Car {
  constructor(brand, mod) {
    super(brand);
    this.model = mod;
  }
  show() {
    return this.present() + ', it is a ' + this.model;
  }
}
```
Getter/setter with an underscore backing field:
```javascript
get carname() { return this._carname; }
set carname(x) { this._carname = x; }
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source.

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.89
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Classes]], [[JavaScript Class Static]], [[JavaScript Objects]], [[JavaScript Object Accessors]]
- **참조 맥락:** Builds on JavaScript Classes by adding inheritance (`extends`/`super`), accessors, and hoisting behavior.

## 📚 출처 (Sources)
- [S1] W3Schools — JavaScript Class Inheritance — https://www.w3schools.com/js/js_class_inheritance.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Class Inheritance" page (Astra wiki-curation, P-Reinforce v3.1 format).