docs(10_Wiki): W3Schools 위키화 — HTML/CSS/JavaScript(core)

W3Schools 튜토리얼을 P-Reinforce v3.1 포맷으로 위키화(영어 본문, 한/영 섹션 헤더).
- Topic_HTML: 59문서 (튜토리얼+예제, 레퍼런스/메타 제외)
- Topic_CSS: 190문서 (메인 + Advanced/Flexbox/Grid/RWD 전체)
- Topic_JavaScript: 120문서 (코어 언어; Temporal/DOM상세/BOM/WebAPI/AJAX/jQuery/Graphics 등은 후속)
각 폴더 00_INDEX.md(MOC) 포함. 코드 verbatim, 미확인분은 "Not found in source" 표기.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

10_Wiki/Topic_JavaScript/JavaScript_Hoisting.md

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+---
+id: javascript-hoisting
+title: "JavaScript Hoisting"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["hoisting", "variable hoisting", "temporal dead zone", "declaration hoisting", "var hoisting"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.87
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "hoisting", "var", "let", "const", "scope"]
+raw_sources: ["https://www.w3schools.com/js/js_hoisting.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript Hoisting]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Hoisting is JavaScript's default behavior of moving all *declarations* (not initializations) to the top of the current scope — so a `var` can be used before it is declared, but `let`/`const` cannot. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Hoisting moves declarations up** — JavaScript moves all declarations to the top of the current scope (the top of the current script or the current function). [S1]
+- **`var` is hoisted and usable early** — a `var` variable can be referenced before its declaration line without error. [S1]
+- **`let` and `const` are hoisted but not initialized** — using them before declaration throws a `ReferenceError` because of the "temporal dead zone"; using `const` before declaration is a syntax error. [S1]
+- **Only declarations hoist, not initializations** — the assignment (`= value`) stays where it is written, so an early-referenced variable reads as `undefined`. [S1]
+- **Best practice** — always declare all variables at the beginning of every scope; strict mode does not allow undeclared variables. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Declare at the top of scope** — to avoid hoisting-related bugs, put all declarations first. [S1]
+- **Never rely on `let`/`const` before declaration** — they live in the temporal dead zone until their declaration line runs. [S1]
+- **Remember: declaration ≠ initialization** — an early read returns `undefined`, not the assigned value. [S1]
+
+## 📖 세부 내용 (Details)
+**What is Hoisting?**
+Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope (to the top of the current script or the current function). [S1]
+
+**`var` Declarations are Hoisted**
+A variable can be used before it has been declared. The following example gives the same result as declaring `x` first: [S1]
+```javascript
+x = 5; // Assign 5 to x
+
+elem = document.getElementById("demo"); // Find an element
+elem.innerHTML = x;                     // Display x in the element
+
+var x; // Declare x
+```
+This is equivalent to: [S1]
+```javascript
+var x; // Declare x
+x = 5; // Assign 5 to x
+
+elem = document.getElementById("demo"); // Find an element
+elem.innerHTML = x;                     // Display x in the element
+```
+
+**`let` and `const` Hoisting**
+Variables defined with `let` and `const` are hoisted to the top of the block, but they are *not* initialized. Using a `let` variable before it is declared results in a `ReferenceError`: [S1]
+```javascript
+carName = "Volvo";
+let carName;
+```
+Using a `const` variable before it is declared is a syntax error, so the code will not run: [S1]
+```javascript
+carName = "Volvo";
+const carName;
+```
+
+**JavaScript Initializations are Not Hoisted**
+JavaScript hoists *declarations*, not *initializations*. Because only the declaration of `y` is hoisted (and not its assignment), `y` is `undefined` when it is first used: [S1]
+```javascript
+var x = 5; // Initialize x
+
+elem = document.getElementById("demo"); // Find an element
+elem.innerHTML = x + " " + y;           // Display x and y
+
+var y = 7; // Initialize y
+```
+
+**Declare Your Variables At the Top**
+To avoid bugs, always declare all variables at the beginning of every scope. Since this is how JavaScript interprets the code, it is a good rule. JavaScript in strict mode does not allow variables to be used if they are not declared. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's examples are the applied cases: showing `var x` usable before its declaration line, the `let`/`const` `ReferenceError`/syntax-error cases, and the `y` value reading as `undefined` because its initialization did not hoist. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+`var` is hoisted (usable before declaration) (language: JavaScript):
+```javascript
+x = 5;
+var x; // Declaration hoisted to top of scope
+```
+`let` before declaration throws:
+```javascript
+carName = "Volvo";
+let carName; // ReferenceError
+```
+Initialization is not hoisted (reads undefined):
+```javascript
+elem.innerHTML = x + " " + y; // y is undefined here
+var y = 7;
+```
+
+## ⚖️ 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:** 0.87
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[JavaScript Tutorial]]
+- **관련 개념:** [[JavaScript var let const]], [[JavaScript Scope]], [[JavaScript Strict Mode]], [[JavaScript Code Blocks]]
+- **참조 맥락:** Explains why variable order matters and motivates declaring variables at the top of each scope.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript Hoisting — https://www.w3schools.com/js/js_hoisting.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Hoisting" page (Astra wiki-curation, P-Reinforce v3.1 format).