2nd/10_Wiki/Topic_JavaScript/JavaScript_Object_Properties.md

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

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-properties	JavaScript Object Properties	Frontend	draft	conceptual		JS object properties dot notation bracket notation delete property in operator nested objects key value pairs		B	0.89	2026-06-23	2026-06-23			javascript js web frontend w3schools objects properties dot-notation	https://www.w3schools.com/js/js_object_properties.asp

JavaScript Object Properties

🎯 한 줄 통찰 (One-line insight)

An object is a collection of key:value properties that can be changed, added, and deleted — accessed by dot notation, bracket notation, or an expression. [S1]

🧠 핵심 개념 (Core concepts)

• Properties are key:value pairs — a JavaScript object is a collection of properties that can be changed, added, and deleted. [S1]
• Three access ways — dot notation, bracket notation, and expression (a name stored in a variable). [S1]
• Dot notation preferred — it is generally preferred for readability and simplicity. [S1]
• Bracket notation when needed — required when the property name is in a variable or is not a valid identifier (e.g. "last-name"). [S1]
• delete removes value and property — after deletion, accessing the property returns undefined. [S1]
• in operator — checks whether a property exists in an object. [S1]
• Nested objects — property values can be other objects, reachable by chaining dot/bracket notation. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Dynamic property access — person[myVariable] resolves a property whose name is held in a variable. [S1]
• Add-by-assignment — assigning to a non-existent property (person.nationality = "English") creates it. [S1]
• Existence check before use — ("firstName" in person) guards access to optional properties. [S1]

📖 세부 내용 (Details)

Properties are key:value Pairs A JavaScript object is a collection of properties. Properties can be changed, added, and deleted. [S1]

Accessing JavaScript Properties You can access object properties by dot notation, bracket notation, or expression: [S1]

// objectName.property
let age = person.age;

// objectName["property"]
let age = person["age"];

// objectName[expression]
let age = person[x];

Dot Notation — objectName.propertyName: [S1]

person.firstname + " is " + person.age;

Bracket Notation — objectName["propertyName"]: [S1]

person["firstname"] + " is " + person["age"];

In general, dot notation is preferred for readability and simplicity. Bracket notation is necessary in some cases: when the property name is stored in a variable (person[myVariable]), or when the property name is not a valid identifier (person["last-name"]). Bracket notation is useful when the property name is stored in a variable: [S1]

let n1 = "firstName";
let n2 = "lastName";

let name = person[n2] + " " + person[n2];

Changing Properties — you can change the value of a property: [S1]

person.age = 10;

Adding New Properties — add a new property by simply giving it a value: [S1]

person.nationality = "English";

Deleting Properties — the delete keyword deletes a property from an object: [S1]

const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50,
};

delete person.age;

const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50,
};

delete person["age"];

The delete keyword deletes both the value and the property. After deleting, the property is removed; accessing it will return undefined. [S1]

Check if a Property Exists — use the in operator: [S1]

const person = {
  firstName: "John",
  lastName: "Doe"
};

let result = ("firstName" in person);

Nested Objects — property values in an object can be other objects: [S1]

myObj = {
  name:"John",
  age:30,
  myCars: {
    car1:"Ford",
    car2:"BMW",
    car3:"Fiat"
  }
}

You can access nested objects using dot notation or bracket notation: [S1]

myObj.myCars.car2;

myObj.myCars["car2"];

myObj["myCars"]["car2"];

let p1 = "myCars";
let p2 = "car2";
myObj[p1][p2];

Summary Object properties are key:value pairs; access properties with dot notation or bracket notation; add, change, and delete properties using assignment and delete; use the in operator to check if a property exists. [S1]

⚖️ 비교 및 선택 기준 (Comparison & decision criteria)

Access style	Use when	Note
Dot notation obj.prop	Default	Preferred for readability and simplicity [S1]
Bracket notation obj["prop"]	Name in a variable, or not a valid identifier	e.g. obj[myVar], obj["last-name"] [S1]

🛠️ 적용 사례 (Applied in summary)

The page's own snippets are the canonical applied examples — accessing person.firstname/person["firstname"], dynamic access via variables, delete person.age, the in check, and nested myObj.myCars.car2 access. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Dynamic property access via a variable:

let n2 = "lastName";
let name = person[n2];

Add then delete a property:

person.nationality = "English";
delete person.age;

Existence check:

let result = ("firstName" in person);

⚖️ 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 Objects, JavaScript Object Methods, JavaScript Object Display
• 참조 맥락: Referenced whenever reading, writing, adding, or removing data on an object.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Object Properties — https://www.w3schools.com/js/js_object_properties.asp

📝 변경 이력 (Change history)

• 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Object Properties" page (Astra wiki-curation, P-Reinforce v3.1 format).