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_Asynchronous.md

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+---
+id: javascript-asynchronous
+title: "JavaScript Asynchronous"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["Async JavaScript", "Asynchronous programming", "JS async overview", "Async study path", "Non-blocking JavaScript"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.86
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "asynchronous", "concurrency"]
+raw_sources: ["https://www.w3schools.com/js/js_asynchronous.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript Asynchronous]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Asynchronous code lets a program start a long-running task and continue with other work before that task finishes, instead of executing strictly one blocking line at a time. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Default flow is synchronous** — JavaScript executes code one line at a time, and each line must finish before the next can run. [S1]
+- **Async changes the order** — async code allows a program to start a long-running task (like fetching data from a file) and continue with other tasks before the first one finishes. [S1]
+- **A learning progression** — the page frames async as a curriculum to "Learn Asynchronous JavaScript in the Right Order," moving from timeouts → callbacks → promises → async/await → fetch → debugging. [S1]
+- **Async ≠ parallel** — parallel means doing multiple things at the same time on different processors; asynchronous means switching between tasks, not necessarily running them simultaneously. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Defer-and-continue** — schedule work to run later (e.g. via a timer) so the current call stack can finish first, producing an out-of-order result such as A, C, B. [S1]
+- **Result-not-ready trap** — reading the result of an async operation immediately yields `undefined` because the async code has not finished yet. [S1]
+- **Restaurant model** — place the order (async call), do other things while it is prepared, and the server brings the food (the callback). [S1]
+
+## 📖 세부 내용 (Details)
+**What is asynchronous code?**
+Async code allows a program to start a long-running task (like fetching data from a file) and continue with other tasks before the first one finishes. By default JavaScript executes from top to bottom, one line at a time; each line must finish before the next can run. Async programming can change this execution order. [S1]
+
+**Synchronous flow**
+Calls run in source order, producing output A, B, C: [S1]
+```javascript
+myDisplayer("A");
+myDisplayer("B");
+myDisplayer("C");
+```
+
+**Asynchronous flow with setTimeout**
+When a timer defers a call, the output order changes to A, C, B — the deferred `B` runs after the synchronous `C`: [S1]
+```javascript
+myDisplayer("A");
+
+setTimeout(function() {
+  myDisplayer("B");
+}, 1000);
+
+myDisplayer("C");
+```
+
+**The "result is not ready yet" challenge**
+Beginners often expect async results immediately. Here the result is `undefined` because the async code has not finished yet: [S1]
+```javascript
+let result;
+
+setTimeout(function() {
+  result = 5;
+}, 1000);
+
+// What is result here?
+```
+
+**Core async concepts**
+The module covers these building blocks: [S1]
+
+| Concept | Description |
+|---------|-------------|
+| Synchronous | The JavaScript standard flow is executing line by line |
+| Timers | Allows code to run while other code is waiting |
+| Callbacks | Callbacks were the first solution for async JavaScript |
+| Events | Stores a callback function waiting to be executed |
+| Promises | Tools to handle asynchronous operations cleanly |
+| Async/Await | The clean and modern way to handle async code |
+
+**Asynchronous vs parallel**
+Parallel means doing multiple things at the same time on different processors. Asynchronous means switching between tasks, not necessarily running them simultaneously. [S1]
+
+**Restaurant analogy**
+Place your order (async call); sit down and do other things while the chef makes it; the server brings the food (the callback). [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page itself is an index/study path; its illustrative snippets (synchronous A/B/C, deferred A/C/B, and the `undefined` result trap) are the canonical applied examples. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Deferring work so later lines run first (language: JavaScript):
+```javascript
+myDisplayer("A");
+
+setTimeout(function() {
+  myDisplayer("B");
+}, 1000);
+
+myDisplayer("C");
+```
+Demonstrating the not-yet-ready result:
+```javascript
+let result;
+
+setTimeout(function() {
+  result = 5;
+}, 1000);
+
+// What is result here?
+```
+
+## ⚖️ 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:** 0.86
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[JavaScript Tutorial]]
+- **관련 개념:** [[JavaScript Async Timeouts]], [[JavaScript Async Callbacks]], [[JavaScript Promise]], [[JavaScript Async Await]], [[JavaScript Async Fetch]]
+- **참조 맥락:** The conceptual entry point for the entire asynchronous JavaScript study path.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript Asynchronous — https://www.w3schools.com/js/js_asynchronous.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Asynchronous" page (Astra wiki-curation, P-Reinforce v3.1 format).