2nd/10_Wiki/Dev/Topic_JavaScript/JavaScript_Primitive_Data.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-primitive-data-types	JavaScript Primitive Data Types	Frontend	draft	conceptual		JS primitives primitive types string number boolean undefined null BigInt		B	0.89	2026-06-23	2026-06-23			javascript js web frontend w3schools primitives data-types string number	https://www.w3schools.com/js/js_datatypes_primitives.asp

JavaScript Primitive Data Types

🎯 한 줄 통찰 (One-line insight)

JavaScript has 7 primitive data types — Number, BigInt, String, Boolean, Undefined, Null, and Symbol — each a simple, immutable value distinct from the single object type. [S1]

🧠 핵심 개념 (Core concepts)

• 7 primitive types — JavaScript variables can hold 7 primitive types (Number, BigInt, String, Boolean, Undefined, Null, Symbol) or 1 object type. [S1]
• Strings — a string is a series of characters, written with single or double quotes. [S1]
• Numbers are 64-bit floats — all JavaScript numbers are stored as double (64-bit floating point) values; they support decimals and exponential notation. [S1]
• BigInt (ES2020) — handles integers too large for standard numbers. [S1]
• Undefined vs Null — a variable without a value is undefined; null represents the intentional absence of a value, but typeof null returns "object" (a historical quirk). [S1]

🧩 추출된 패턴 (Extracted patterns)

• Nest opposite quotes — put single quotes inside double-quoted strings (and vice versa) to avoid escaping. [S1]
• === vs == for null/undefined — strict equality (===) is true only when value and type match; loose equality (==) treats null and undefined as equal. [S1]
• Empty string is still a string — let car = ""; has value "" and typeof "string". [S1]

📖 세부 내용 (Details)

JavaScript variables can hold 8 types of data: 7 primitive types or 1 object type. The primitive types are: Number, BigInt, String, Boolean, Undefined, Null, and Symbol. [S1]

JavaScript Strings A string is a series of characters like "John Doe", written with single or double quotes. [S1]

// Using double quotes:
let carName1 = "Volvo XC60";

// Using single quotes:
let carName2 = 'Volvo XC60';

You can nest the opposite quote type inside a string: [S1]

// Single quote inside double quotes:
let answer1 = "It's alright";

// Single quotes inside double quotes:
let answer2 = "He is called 'Johnny'";

// Double quotes inside single quotes:
let answer3 = 'He is called "Johnny"';

JavaScript Numbers All JavaScript numbers are stored as decimal (floating point) values — always double (64-bit floating point). [S1]

// With decimals:
let x1 = 34.00;

// Without decimals:
let x2 = 34;

Exponential notation: [S1]

let y = 123e5;    // 12300000
let z = 123e-5;   // 0.00123

JavaScript BigInt BigInt (ES2020) handles integers too large for standard numbers: [S1]

let x = BigInt("123456789012345678901234567890");

JavaScript Booleans Booleans can only hold true or false: [S1]

let x = 5;
let y = 5;
let z = 6;
(x == y)       // Returns true
(x == z)       // Returns false

The typeof Operator The typeof operator identifies a variable's type. [S1]

typeof ""             // Returns "string"
typeof "John"         // Returns "string"
typeof "John Doe"     // Returns "string"

typeof 0              // Returns "number"
typeof 314            // Returns "number"
typeof 3.14           // Returns "number"
typeof (3)            // Returns "number"
typeof (3 + 4)        // Returns "number"

Undefined A variable without a value has the value undefined and the type undefined: [S1]

let car;    // Value is undefined, type is undefined

car = undefined;    // Value is undefined, type is undefined

Empty Values An empty string has both a legal value and a type: [S1]

let car = "";    // The value is "", the typeof is "string"

Datatype null null represents "nothing" — the intentional absence of a value: [S1]

let carName = null;

Notes on null: the typeof operator returns "object" for null (a historical quirk); the strict equality operator === returns true only if both value and type match; the loose equality operator == returns true for both null and undefined. [S1]

🛠️ 적용 사례 (Applied in summary)

The page's own declarations (string quoting variants, number/exponent/BigInt literals, boolean comparisons, and the undefined/empty/null examples) are the canonical applied examples. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Nest opposite quotes (language: JavaScript):

let answer1 = "It's alright";
let answer3 = 'He is called "Johnny"';

Exponential number notation:

let y = 123e5;    // 12300000
let z = 123e-5;   // 0.00123

⚖️ 모순 및 업데이트 (Contradictions & updates)

typeof null returns "object" even though null is a primitive value — the page flags this as a historical quirk. BigInt was introduced in ES2020. [S1]

✅ 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 Data Types, JavaScript Object Data Types, JavaScript typeof, JavaScript Symbols
• 참조 맥락: Referenced whenever declaring simple values or reasoning about equality and typeof results.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Primitive Data Types — https://www.w3schools.com/js/js_datatypes_primitives.asp

📝 변경 이력 (Change history)

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