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_Maps.md

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+---
+id: javascript-maps
+title: "JavaScript Maps"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["Map", "new Map", "key-value pairs", "ES6 Map", "Map.set", "Map.get", "dictionary"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.9
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "map", "collection", "es6"]
+raw_sources: ["https://www.w3schools.com/js/js_maps.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript Maps]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+A JavaScript Map stores key-value pairs like a dictionary, but unlike plain objects its keys can be of any data type, it remembers insertion order, and it exposes a `size` property. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **A Map is an object that stores key-value pairs**, similar to a dictionary in other languages; keys can be of any data type. [S1]
+- **Maps are most similar to Objects** (a unique key/value collection), but with stronger guarantees. [S1]
+- **Six characteristics** — keys can be any type; original insertion order is remembered; item count is easy via `size`; optimized for frequent additions/removals; directly iterable with `for...of` or `forEach()`; original order preserved during iteration. [S1]
+- **Two ways to create a Map** — `new Map()` then `set()` calls, or `new Map([...])` with an array of `[key, value]` pairs. [S1]
+- **`set()` adds or updates** — calling `set()` with an existing key changes its value. [S1]
+- **`get()` retrieves a value** by its key. [S1]
+- **Type identity** — `typeof` a Map returns `"object"`, and `instanceof Map` returns `true`. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **set-chain construction** — create empty, then `set()` each pair. [S1]
+- **Array-literal construction** — pass `[[k, v], ...]` to `new Map()`. [S1]
+- **Upsert by key** — `set()` doubles as insert (new key) and update (existing key). [S1]
+
+## 📖 세부 내용 (Details)
+A JavaScript Map is an object that can store collections of key-value pairs, similar to a dictionary in other programming languages. Maps differ from standard objects in that keys can be of any data type. Maps are similar to both Objects (unique key/value collection) and Arrays (ordered values collection), but Maps are most similar to Objects. [S1]
+
+**Map characteristics:** keys can be any type; the original insertion order is remembered; the number of items is easily retrieved via the `size` property; optimized for frequent additions and removals; directly iterable with `for...of` loops or `forEach()`; original order preserved during iteration. [S1]
+
+**How to Create a Map** — you can create a Map by passing an Array to `new Map()`, or by creating a Map and using `set()`. [S1]
+
+**Using set()** — create an empty Map and set values: [S1]
+```javascript
+// Create an empty Map
+const fruits = new Map();
+
+// Set Map Values
+fruits.set("apples", 500);
+fruits.set("bananas", 300);
+fruits.set("oranges", 200);
+```
+
+**Using an Array** — pass an array of `[key, value]` pairs to the constructor: [S1]
+```javascript
+// Create a Map
+const fruits = new Map([
+  ["apples", 500],
+  ["bananas", 300],
+  ["oranges", 200]
+]);
+```
+
+**Adding Elements** — the `set()` method can also be used to add new elements: [S1]
+```javascript
+fruits.set("mangos", 100);
+```
+
+**Changing Values** — `set()` will also change existing values: [S1]
+```javascript
+fruits.set("apples", 200);
+```
+
+**The get() Method** — gets the value of a key: [S1]
+```javascript
+fruits.get("apples");    // Returns 500
+```
+
+**A JavaScript Map is an Object** [S1]
+```javascript
+// Returns object:
+typeof fruits;
+```
+```javascript
+// Returns true:
+fruits instanceof Map;
+```
+
+**JavaScript Objects vs Maps** [S1]
+
+| | Object | Map |
+|---|--------|-----|
+| Iterable | Not directly iterable | Directly iterable |
+| Size property | Do not have a size property | Have a size property |
+| Key types | Keys must be Strings (or Symbols) | Keys can be any datatype |
+| Key ordering | Keys are not well ordered | Keys are ordered by insertion |
+| Default keys | Have default keys | Do not have default keys |
+
+**Browser Support** — Map is an ES6 feature (JavaScript 2015), fully supported in all modern browsers since June 2017. [S1]
+
+| Browser | Version | Release |
+|---------|---------|---------|
+| Chrome | 51 | May 2016 |
+| Edge | 15 | Apr 2017 |
+| Firefox | 54 | Jun 2017 |
+| Safari | 10 | Sep 2016 |
+| Opera | 38 | Jun 2016 |
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's own snippets are the canonical applied examples — building a `fruits` Map by `set()` calls or array literal, adding `mangos`, updating `apples`, and reading back with `get()`. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Create a Map from an array of pairs (language: JavaScript):
+```javascript
+const fruits = new Map([
+  ["apples", 500],
+  ["bananas", 300],
+  ["oranges", 200]
+]);
+```
+Upsert and read:
+```javascript
+fruits.set("apples", 200);
+fruits.get("apples");
+```
+
+## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
+Per the source's Objects-vs-Maps table, prefer a Map over a plain Object when you need: direct iterability (`for...of`), a built-in `size`, keys of any data type (not just strings/symbols), reliable insertion ordering, or no inherited default keys. Use a plain Object for simple string-keyed records where those guarantees are not required. [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:** 0.90
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[JavaScript Tutorial]]
+- **관련 개념:** [[JavaScript Map Methods]], [[JavaScript Sets]], [[JavaScript Set Methods]]
+- **참조 맥락:** The base concept referenced whenever an ordered, any-key key-value collection is needed.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript Maps — https://www.w3schools.com/js/js_maps.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Maps" page (Astra wiki-curation, P-Reinforce v3.1 format).