docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합
이전 재구성 작업에서 Dev/ 폴더가 누락되었던 것을 반영. - Dev/Topic_Programming(중첩 폴더, 78개)은 Dev 자체 최상위 폴더들 (Architecture/Conventions/Engineering_Intelligence 등)과 완전 중복이라 제거. - Dev 최상위 엔지니어링 지식 폴더(Architecture/Conventions/Engineering_Intelligence/ Failure_Library/Generalized_Principles/Language/Pattern_Catalog/Platform_Guides/ Subsystems, 77개)는 이미 Topic_Programming/Topic_Programming에 더 최신 버전이 존재해 중복 제거(고유 콘텐츠 1개는 예외 처리하여 이동 보존). - Dev의 W3Schools 언어 튜토리얼 폴더(Topic_C/CPP/CSS/CSharp/HOWTO/HTML/Java/ JavaScript/PHP/Python/SQL/W3CSS, 1201개)는 전부 Topic_Programming 하위로 이동. - 에이전트 운영 상태(.astra/docs)는 그대로 유지, 콘텐츠 폴더만 정리. - Topic_Programming 최종 문서 수: 2784 → 3985.
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Antigravity Agent
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---
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id: javascript-async
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title: "JavaScript Async"
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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: ["Async programming", "JS async basics", "Synchronous vs asynchronous", "Async execution order", "Non-blocking code"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.87
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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", "asynchronous", "settimeout"]
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raw_sources: ["https://www.w3schools.com/js/js_async.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[JavaScript Async]]
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## 🎯 한 줄 통찰 (One-line insight)
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JavaScript runs line by line by default, but async code can start a long-running task and keep working — so the visible order of results may differ from the source order. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Default execution is top-to-bottom, left-to-right** — JavaScript normally executes one line at a time in source order. [S1]
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- **Async reorders work** — async code lets a program start a long-running task (like fetching data from a file) and continue with other tasks before the first finishes, which can change the execution order. [S1]
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- **The result-not-ready problem** — reading an async result too early yields `undefined` because the async code has not finished yet. [S1]
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- **Async is not parallel** — parallel runs multiple things simultaneously on different processors; async switches between tasks without necessarily running them at the same time. [S1]
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- **Six building blocks** — synchronous flow, timers, callbacks, events, promises, and async/await. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Order swap by call order** — calling `mySecond()` before `myFirst()` simply changes which output appears first; ordinary synchronous calls obey source order. [S1]
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- **Deferred call via setTimeout** — wrapping a call in `setTimeout(fn, ms)` pushes it after the synchronous lines, yielding A, C, B. [S1]
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- **Event-driven callback** — an HTML attribute like `onclick` wires user interaction to a function that runs later. [S1]
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## 📖 세부 내용 (Details)
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**Synchronous calls run in order**
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Plain calls produce output A, B, C: [S1]
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```javascript
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myDisplayer("A");
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myDisplayer("B");
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myDisplayer("C");
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```
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**Function order matters**
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Defining two functions and calling them in order: [S1]
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```javascript
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function myFirst() {
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myDisplayer("Hello");
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}
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function mySecond() {
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myDisplayer("Goodbye");
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}
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myFirst();
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mySecond();
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```
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Swapping the call order swaps the output: [S1]
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```javascript
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function myFirst() {
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myDisplayer("Hello");
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}
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function mySecond() {
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myDisplayer("Goodbye");
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}
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mySecond();
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myFirst();
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```
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**Asynchronous flow with setTimeout**
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The deferred `B` runs after the synchronous `C`, so the order is A, C, B: [S1]
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```javascript
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myDisplayer("A");
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setTimeout(function() {
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myDisplayer("B");
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}, 1000);
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myDisplayer("C");
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```
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**The result-not-ready trap**
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The result is `undefined` because the async code has not finished yet: [S1]
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```javascript
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let result;
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setTimeout(function() {
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result = 5;
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}, 1000);
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// What is result here?
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```
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**JavaScript events**
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Events wire callbacks to user interaction: [S1]
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```javascript
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<button onclick="displayDate()">The time is?</button>
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```
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**Core async concepts**
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[S1]
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| Concept | Description |
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|---------|-------------|
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| Synchronous | The JavaScript standard flow is executing line by line |
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| Timers | Allows code to run while other code is waiting |
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| Callbacks | Callbacks were the first solution for async JavaScript |
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| Events | Stores a callback function waiting to be executed |
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| Promises | Tools to handle asynchronous operations cleanly |
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| Async/Await | The clean and modern way to handle async code |
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**Asynchronous vs parallel**
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Parallel means doing multiple things at the same time on different processors. Asynchronous means switching between tasks, not necessarily running them simultaneously. [S1]
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**Restaurant analogy**
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Place your order (async call); sit down and do other things while the chef makes it; the server brings the food (the callback). [S1]
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own snippets — ordered/reordered function calls, the deferred A/C/B `setTimeout`, the `undefined` result trap, and the `onclick` event button — are the canonical applied examples. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Deferred execution that reorders output (language: JavaScript):
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```javascript
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myDisplayer("A");
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setTimeout(function() {
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myDisplayer("B");
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}, 1000);
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myDisplayer("C");
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```
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Event-driven callback:
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```javascript
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<button onclick="displayDate()">The time is?</button>
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```
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source.
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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:** 0.87
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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 Asynchronous]], [[JavaScript Async Timeouts]], [[JavaScript Async Callbacks]], [[JavaScript Promise]]
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- **참조 맥락:** The foundational lesson establishing why execution order matters before introducing timeouts, callbacks, and promises.
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## 📚 출처 (Sources)
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- [S1] W3Schools — JavaScript Async — https://www.w3schools.com/js/js_async.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Async" page (Astra wiki-curation, P-Reinforce v3.1 format).
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