refactor(topics): 멀티 에이전트용 지식 재편 — _Common(공통 기본기) + Domain_* 구조
에이전트 8종(대화형/프로그래머 C·S/디자이너/설계자/기획자/QA/PD/PM)에게 [공통 기본 능력 + 롤별 Specialty] 2층으로 지식을 주입하기 위한 재분류. 문서 내용·포맷은 무수정, 폴더 이동만 (6,372개 문서 수 보존 확인). - Topic_Programming → Domain_Programming (내부 구조 보존) - Topic_Graphic → Domain_Design - Topic_Business → Domain_Product - Topic_General → Domain_General - _Common 신설: Math(구 Topic_Math_Specialty), Reasoning(구 General/From_Thinking & Reasoning), Reasoning_Creativity(구 General/From_창의성), Communication(Poetic_Blog_Writing + From_writing) - 타 도메인의 From_* 폴더는 유지 (출처 표기일 뿐, 이미 도메인에 맞게 분류된 문서) - 빈 폴더 정리 (memory/procedures) - 에이전트→폴더 매핑은 workspace의 .astra/agent-knowledge-map.json (9개 에이전트) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Antigravity Agent
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---
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id: javascript-let
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title: "JavaScript Let"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["let keyword", "block scope", "let vs var", "let hoisting", "ES6 let"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.88
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["javascript", "js", "web", "frontend", "w3schools", "let", "block-scope"]
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raw_sources: ["https://www.w3schools.com/js/js_let.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[JavaScript Let]]
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## 🎯 한 줄 통찰 (One-line insight)
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The `let` keyword (ES6, 2015) introduced block scope to JavaScript — `let` variables are confined to their `{ }` block, cannot be redeclared in the same scope, and are hoisted but not initialized. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Block scope (new in ES6)** — before ES6 (2015) JavaScript had no block scope; variables declared with `let` inside a `{ }` block cannot be accessed outside it. [S1]
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- **Function scope** — variables declared with `var`, `let`, or `const` inside a function cannot be accessed outside it. [S1]
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- **`var` is global/function scoped** — a `var` declared inside a block can still be used outside the block. [S1]
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- **Cannot be redeclared in the same scope** — `let` variables cannot be redeclared in the same scope (whereas `var` can). [S1]
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- **Hoisted but not initialized** — `let` variables are hoisted to the top of their block but not initialized; using one before its declaration causes a `ReferenceError`. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Block-local shadowing** — declaring `let x` inside a block shadows an outer `x` without altering it, unlike `var` which leaks back out. [S1]
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- **Redeclare across different blocks** — the same `let` name may be redeclared in different blocks, just not twice in the same scope. [S1]
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- **Declare-before-use discipline** — because `let` is not initialized when hoisted, always declare before using. [S1]
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## 📖 세부 내용 (Details)
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**Block Scope** — Before ES6 (2015), JavaScript had only Global Scope and Function Scope. ES6 introduced two new JavaScript keywords: `let` and `const`. These two keywords provided Block Scope in JavaScript. Variables declared inside a `{ }` block cannot be accessed from outside the block: [S1]
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```javascript
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{
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let x = 2;
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}
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// x can NOT be used here
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```
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**Function Scope** — Variables declared with `var`, `let`, and `const` are quite similar when declared inside a function — they all have Function Scope: [S1]
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```javascript
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function myfunction() {
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var x = 1;
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let y = 2;
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const z = 3;
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}
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//x can NOT be used here
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//y can NOT be used here
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//z can NOT be used here
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```
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**Global Scope (var)** — Variables declared with `var` inside a block can be accessed from outside the block: [S1]
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```javascript
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{
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var x = 2;
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}
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// x CAN be used here
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```
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**Cannot be Redeclared** — Variables defined with `let` can not be redeclared. You can not accidentally redeclare a variable declared with `let`: [S1]
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```javascript
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let x = "John Doe";
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let x = 0; // Error
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```
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Variables defined with `var` can be redeclared: [S1]
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```javascript
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var x = "John Doe";
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var x = 0; // Allowed
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```
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**Redeclaring Variables** — Redeclaring a variable using the `var` keyword can impose problems. Redeclaring a variable inside a block will also redeclare the variable outside the block: [S1]
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```javascript
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var x = 10;
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// Here x is 10
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{
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var x = 2;
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// Here x is 2
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}
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// Here x is 2
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```
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Redeclaring a variable using the `let` keyword can solve this problem. Redeclaring a variable inside a block will not redeclare the variable outside the block: [S1]
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```javascript
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let x = 10;
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// Here x is 10
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{
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let x = 2;
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// Here x is 2
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}
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// Here x is 10
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```
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**Redeclaring (across different blocks)** — Redeclaring a `let` variable in different blocks is allowed: [S1]
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```javascript
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let x = 2; // Allowed
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{
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let x = 3; // Allowed
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}
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{
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let x = 4; // Allowed
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}
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```
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**Let Hoisting** — Variables defined with `let` are hoisted to the top of the block, but not initialized. Using a `let` variable before it is declared will result in a `ReferenceError`: [S1]
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```javascript
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carName = "Saab";
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let carName = "Volvo"; // ReferenceError
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```
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By contrast, variables defined with `var` are hoisted to the top and can be used before declaration: [S1]
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```javascript
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carName = "Volvo";
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var carName; // OK
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```
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own snippets are the canonical applied examples — block-scoped `let x`, the `var`-leaks vs `let`-contained redeclaration pair, redeclaring `let` across separate blocks, and the hoisting `ReferenceError` contrast. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Block-scoped variable:
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```javascript
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{
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let x = 2;
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}
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// x can NOT be used here
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```
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Safe shadowing:
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```javascript
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let x = 10;
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{
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let x = 2;
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}
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// Here x is 10
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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The source compares the three declaration keywords: [S1]
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| Feature | var | let | const |
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|---------|-----|-----|-------|
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| Scope | Function or global | Block-scope `{ }` | Block-scope `{ }` |
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| Reassignment | Can be updated | Can be updated | Cannot be updated |
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| Redeclaration | Can be redeclared | Cannot be redeclared | Cannot be redeclared |
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| Hoisting | Initialized as `undefined` | Hoisted, not initialized | Hoisted, not initialized |
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Choose `let` when you need a reassignable variable scoped to a block; choose `const` when the value will not change; avoid `var` to prevent unintentional global/function-scope leakage. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source. (The page frames `let`/`const` as a 2015 update over the older `var`-only model — an evolution, not a contradiction.)
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.88
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[JavaScript Tutorial]]
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- **관련 개념:** [[JavaScript Variables]], [[JavaScript Const]], [[JavaScript Statements]]
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- **참조 맥락:** The block-scoped declaration keyword, contrasted against `var` and paired with `const`.
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## 📚 출처 (Sources)
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- [S1] W3Schools — JavaScript Let — https://www.w3schools.com/js/js_let.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Let" page (Astra wiki-curation, P-Reinforce v3.1 format).
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