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_Scope.md

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+---
+id: javascript-scope
+title: "JavaScript Scope"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["variable scope", "global scope", "function scope", "block scope", "local variables"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.88
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "scope", "variables", "let", "const", "var"]
+raw_sources: ["https://www.w3schools.com/js/js_scope.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript Scope]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Scope determines the accessibility (visibility) of variables — JavaScript has three kinds: global, function, and block. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Scope = accessibility** — scope determines where variables are visible and reachable in your code. [S1]
+- **Three scopes** — JavaScript has global scope, function scope, and (since ES6) block scope. [S1]
+- **`let` and `const` are block scoped** — variables declared with `let` and `const` inside a block `{ }` cannot be accessed outside it; `var` is *not* block scoped. [S1]
+- **Function scope applies to all three keywords** — `var`, `let`, and `const` are all function-scoped when declared inside a function and cannot be accessed from outside. [S1]
+- **Automatic globals are a trap** — assigning a value to an undeclared variable makes it a global automatically, which is discouraged; strict mode prevents it. [S1]
+- **Lifetime** — local (function) variables live only while the function runs; global variables live until the page/browser closes. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Declare in the narrowest scope** — keep variables local to the function or block that uses them. [S1]
+- **Prefer block scope for safety** — use `let`/`const` inside blocks to confine variables and avoid leaks. [S1]
+- **Avoid undeclared assignment** — always declare before assigning to avoid creating accidental globals. [S1]
+
+## 📖 세부 내용 (Details)
+**What is scope?**
+Scope determines the accessibility (visibility) of variables. JavaScript has 3 types of scope: Block scope, Function scope, and Global scope. [S1]
+
+**Global Scope**
+Variables declared *outside* any function or block have global scope and can be accessed everywhere, whether declared with `var`, `let`, or `const`: [S1]
+```javascript
+let carName = "Volvo";
+// code here can use carName
+
+function myFunction() {
+  // code here can also use carName
+}
+```
+
+**Function Scope (Local Scope)**
+Variables declared inside a function are local to that function and cannot be accessed from outside. Each function creates a new scope, and all three declaration keywords behave the same way here: [S1]
+```javascript
+function myFunction1() {
+  var carName = "Volvo";   // Function Scope
+}
+
+function myFunction2() {
+  let carName = "Volvo";   // Function Scope
+}
+
+function myFunction3() {
+  const carName = "Volvo"; // Function Scope
+}
+```
+
+**Block Scope**
+Before ES6 (2015), JavaScript had only global scope and function scope. ES6 introduced `let` and `const`, which provide block scope. Variables declared inside a `{ }` block with `let` or `const` cannot be accessed from outside the block: [S1]
+```javascript
+{
+  let x = 2;
+}
+// x can NOT be used here
+```
+Variables declared with `var` do *not* have block scope and *can* be accessed outside the block: [S1]
+```javascript
+{
+  var x = 2;
+}
+// x CAN be used here
+```
+
+**Automatically Global**
+If you assign a value to a variable that has not been declared, it automatically becomes a global variable. This is discouraged. [S1]
+
+**Strict Mode**
+In "strict mode", undeclared variables are not automatically global. [S1]
+
+**The Lifetime of JavaScript Variables**
+The lifetime of a JavaScript variable starts when it is declared. Function (local) variables are deleted when the function completes. Global variables are deleted when you close the page (or browser window). [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's own snippets illustrate the rule directly: the same `carName` variable visible globally vs. confined inside `myFunction1/2/3`, and the contrast between `let x` (block scoped) and `var x` (leaks out of the block). No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Block scope with `let`/`const` (language: JavaScript):
+```javascript
+{
+  let x = 2;
+}
+// x can NOT be used here
+```
+`var` ignores block scope:
+```javascript
+{
+  var x = 2;
+}
+// x CAN be used here
+```
+
+## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
+- **`var` vs. `let`/`const` for block scope** — only `let` and `const` are confined to the block; `var` escapes to the enclosing function/global scope. Choose `let`/`const` to limit visibility. [S1]
+- **Global vs. local** — declare globally only when the value must be shared everywhere; otherwise keep variables local for shorter lifetime and fewer collisions. [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 var let const]], [[JavaScript Code Blocks]], [[JavaScript Hoisting]], [[JavaScript Strict Mode]]
+- **참조 맥락:** Underpins decisions about where to declare variables and which keyword to use.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript Scope — https://www.w3schools.com/js/js_scope.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Scope" page (Astra wiki-curation, P-Reinforce v3.1 format).