2nd/10_Wiki/Topic_JavaScript/JavaScript_Primitive_Data.md

---
id: javascript-primitive-data-types
title: "JavaScript Primitive Data Types"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["JS primitives", "primitive types", "string number boolean", "undefined null", "BigInt"]
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", "primitives", "data-types", "string", "number"]
raw_sources: ["https://www.w3schools.com/js/js_datatypes_primitives.asp"]
applied_in: []
github_commit: ""
---

# [[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]
```javascript
// 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]
```javascript
// 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]
```javascript
// With decimals:
let x1 = 34.00;

// Without decimals:
let x2 = 34;
```
Exponential notation: [S1]
```javascript
let y = 123e5;    // 12300000
let z = 123e-5;   // 0.00123
```

**JavaScript BigInt**
BigInt (ES2020) handles integers too large for standard numbers: [S1]
```javascript
let x = BigInt("123456789012345678901234567890");
```

**JavaScript Booleans**
Booleans can only hold `true` or `false`: [S1]
```javascript
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]
```javascript
typeof ""             // Returns "string"
typeof "John"         // Returns "string"
typeof "John Doe"     // Returns "string"
```
```javascript
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]
```javascript
let car;    // Value is undefined, type is undefined
```
```javascript
car = undefined;    // Value is undefined, type is undefined
```

**Empty Values**
An empty string has both a legal value and a type: [S1]
```javascript
let car = "";    // The value is "", the typeof is "string"
```

**Datatype null**
`null` represents "nothing" — the intentional absence of a value: [S1]
```javascript
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):
```javascript
let answer1 = "It's alright";
let answer3 = 'He is called "Johnny"';
```
Exponential number notation:
```javascript
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).