2nd/10_Wiki/Topic_JavaScript/JavaScript_Object_Constructors.md

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

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]

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]

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]

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]

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]

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]

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]

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):

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:

Person.prototype.nationality = "English";

Add a method:

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).