---
id: javascript-object-constructors
title: "JavaScript Object Constructors"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["Object constructor function", "constructor function", "new keyword", "Person constructor", "prototype property"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools", "objects", "constructors", "prototype"]
raw_sources: ["https://www.w3schools.com/js/js_object_constructors.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Object Constructors]]

## 🎯 한 줄 통찰 (One-line insight)
A constructor function is a reusable "object type" blueprint: call it with `new` to stamp out many objects of the same kind, where `this` becomes each new object. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Constructor functions are object blueprints** — when you need many objects of the same type, define a constructor function and create instances with the `new` keyword. [S1]
- **Naming convention** — it is considered good practice to name constructor functions with an upper-case first letter (e.g. `Person`). [S1]
- **`this` inside a constructor** — `this` has no value of its own; it becomes the new object being created when the function is invoked with `new`. [S1]
- **Prototype changes affect all instances** — a property or method added to `Constructor.prototype` is shared by every object created from that constructor, whereas a property added to one object affects only that object. [S1]
- **Use literals over built-in constructors** — JavaScript has built-in constructors (`new Object()`, `new Array()`, etc.), but the recommended best practice is to use the literal forms instead. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Capitalized constructor + `new`** — define `function Person(...) { this.x = ... }` and instantiate with `const p = new Person(...)`. [S1]
- **Default property in the constructor** — assign a constant property inside the constructor body (`this.nationality = "English";`) so every instance gets it. [S1]
- **Per-object vs. shared** — `obj.prop = value` adds to one object; `Constructor.prototype.prop = value` adds to all. [S1]
- **Method as a property** — attach a function expression to `this` (`this.fullName = function() {...}`) to give instances a method. [S1]

## 📖 세부 내용 (Details)
**Object Type (constructor function)**
When you want to create many objects of the same type, you can use an object constructor function. It is considered good practice to name constructor functions with an upper-case first letter. The example below defines a `Person` object type: [S1]
```javascript
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}
```

**Creating objects with `new`**
Once the object type exists, you create new objects of that type with the `new` keyword: [S1]
```javascript
const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");
const mySister = new Person("Anna", "Rally", 18, "green");
const mySelf = new Person("Johnny", "Rally", 22, "green");
```

**Property Default Values**
A value assigned to a property inside the constructor becomes a default value for all objects created from it: [S1]
```javascript
function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
  this.nationality = "English";
}
```

**Adding a Property to an Object**
Adding a property to a created object is easy, but it is added only to that single object — not to other objects of the same type: [S1]
```javascript
myFather.nationality = "English";
```

**Adding a Property via Prototype**
Adding a property to the constructor's prototype adds it to all objects created from the constructor: [S1]
```javascript
Person.prototype.nationality = "English";
```

**Constructor Method**
A method is a function defined as a property of the object. Methods can be defined inside the constructor: [S1]
```javascript
function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
  this.fullName = function() {
    return this.firstName + " " + this.lastName;
  };
}
```

**Built-in JavaScript Constructors**
JavaScript has built-in constructors for native objects: [S1]
```javascript
new Object();   // A new Object object
new Array();    // A new Array object
new Map();      // A new Map object
new Set();      // A new Set object
new Date();     // A new Date object
new RegExp();   // A new RegExp object
new Function(); // A new Function object
```
Best practice: there is no reason to use these built-in constructors. Use the literal equivalents instead — `{}` for `new Object()`, `[]` for `new Array()`, `/()/` for `new RegExp()`, and `function (){}` for `new Function()`. [S1]

## 🛠️ 적용 사례 (Applied in summary)
The page's `Person` examples are the canonical applied use: defining an object type once and creating multiple instances (`myFather`, `myMother`, `mySister`, `mySelf`) from it, then extending them with default properties, prototype properties, and methods. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Define a constructor and instantiate (language: JavaScript):
```javascript
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}
const myFather = new Person("John", "Doe", 50, "blue");
```
Share across all instances via prototype:
```javascript
Person.prototype.nationality = "English";
```
Add a method:
```javascript
this.fullName = function() {
  return this.firstName + " " + this.lastName;
};
```

## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
- **Constructor vs. object literal** — use a constructor function when you need *many* objects of the same type; for a one-off object, a literal `{}` is simpler. [S1]
- **Per-object property vs. prototype property** — add to the object directly for an instance-specific value; add to the prototype to share across all instances. [S1]
- **Built-in constructor vs. literal** — prefer literals (`{}`, `[]`, `/()/`, `function(){}`) over `new Object()`, `new Array()`, etc. [S1]

## ⚖️ 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:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Objects]], [[JavaScript Object Properties]], [[JavaScript Object Methods]], [[JavaScript Object Prototypes]]
- **참조 맥락:** Referenced whenever you need a reusable object template instead of a single object literal.

## 📚 출처 (Sources)
- [S1] W3Schools — JavaScript Object Constructors — https://www.w3schools.com/js/js_object_constructors.asp

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