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>
2026-06-23 19:21:18 +09:00
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+---
+id: javascript-async-await
+title: "JavaScript Async Await"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["async await", "await keyword", "async function", "try catch await", "Promise.all"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.89
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "async-await", "promises"]
+raw_sources: ["https://www.w3schools.com/js/js_async_await.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript Async Await]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+`async` and `await` make promises easier by letting you write asynchronous code like normal step-by-step code, with familiar `try...catch` error handling. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **They simplify promises** — `async` and `await` make promises easier by letting code be written like normal step-by-step code. [S1]
+- **`async` returns a promise** — an `async` function returns a promise; its return value is what the promise resolves to. [S1]
+- **`await` unwraps a promise** — `await` pauses inside the async function until the awaited promise resolves, giving back the value directly. [S1]
+- **Error handling with try...catch** — wrap awaited calls in `try { ... } catch (error) { ... }` to handle rejections. [S1]
+- **Sequential vs parallel** — awaiting one call after another runs them in sequence; `Promise.all([...])` runs them together and awaits all. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Linearize a promise chain** — replace `.then()` chaining with successive `await` calls inside an `async function`. [S1]
+- **try/catch around await** — catch a rejected promise (e.g. `await fail()`) like a synchronous error. [S1]
+- **Promise.all for parallelism** — start promises first, then `await Promise.all([p1, p2])` to collect results together. [S1]
+
+## 📖 세부 내용 (Details)
+**Promises approach (before)**
+[S1]
+```javascript
+// Three functions to run in steps
+function step1() {
+  return Promise.resolve("A");
+}
+function step2(value) {
+  return Promise.resolve(value + "B");
+}
+function step3(value) {
+  return Promise.resolve(value + "C");
+}
+
+// Run the three functions in steps
+step1()
+.then(function(value) {
+  return step2(value);
+})
+.then(function(value) {
+  return step3(value);
+})
+.then(function(value) {
+  myDisplayer(value);
+});
+```
+
+**async/await approach (after)**
+The same logic reads like sequential code: [S1]
+```javascript
+// Function to run the three functions in steps
+async function run() {
+  let v1 = await step1();
+  let v2 = await step2(v1);
+  let v3 = await step3(v2);
+  myDisplayer(v3);
+}
+
+run();
+```
+
+**The async keyword**
+An `async` function returns a promise: [S1]
+```javascript
+async function myFunction() {
+  return "Hello";
+}
+myFunction().then(
+  function(value) {myDisplayer(value);}
+);
+```
+
+**The await keyword**
+`await` waits for a promise and returns its resolved value: [S1]
+```javascript
+function step1() {
+  return Promise.resolve("A");
+}
+
+async function run() {
+  let value = await step1();
+  myDisplayer(value);
+}
+
+run();
+```
+
+**Error handling with try...catch**
+[S1]
+```javascript
+function fail() {
+  return Promise.reject("Failed");
+}
+
+async function run() {
+  try {
+    let value = await fail();
+    console.log(value);
+  } catch (error) {
+    console.log(error);
+  }
+}
+
+run();
+```
+
+**Sequential execution**
+[S1]
+```javascript
+async function run() {
+  let a = await step1();
+  let b = await step2();
+  console.log(a, b);
+}
+```
+
+**Parallel with Promise.all()**
+Start the promises first, then await them together: [S1]
+```javascript
+async function run() {
+  let p1 = step1();
+  let p2 = step2();
+  let values = await Promise.all([p1, p2]);
+  console.log(values);
+}
+```
+
+**fetch() with async/await**
+[S1]
+```javascript
+async function loadData() {
+  try {
+    let response = await fetch("data.json");
+    let data = await response.json();
+    console.log(data);
+  } catch (error) {
+    console.log(error);
+  }
+}
+
+loadData();
+```
+
+**Basic syntax with a Promise**
+Awaiting a constructed promise: [S1]
+```javascript
+async function myDisplay() {
+  let myPromise = new Promise(function(resolve, reject) {
+    resolve("I love You !!");
+  });
+  document.getElementById("demo").innerHTML = await myPromise;
+}
+
+myDisplay();
+```
+Without the reject parameter: [S1]
+```javascript
+async function myDisplay() {
+  let myPromise = new Promise(function(resolve) {
+    resolve("I love You !!");
+  });
+  document.getElementById("demo").innerHTML = await myPromise;
+}
+
+myDisplay();
+```
+
+**Waiting for a timeout**
+[S1]
+```javascript
+async function myDisplay() {
+  let myPromise = new Promise(function(resolve) {
+    setTimeout(function() {resolve("I love You !!");}, 3000);
+  });
+  document.getElementById("demo").innerHTML = await myPromise;
+}
+
+myDisplay();
+```
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's snippets — the `run()` function linearizing step1/step2/step3, the `try...catch` around `await fail()`, and `await Promise.all([p1, p2])` — are the canonical applied examples. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Linearize a chain with await (language: JavaScript):
+```javascript
+async function run() {
+  let v1 = await step1();
+  let v2 = await step2(v1);
+  let v3 = await step3(v2);
+  myDisplayer(v3);
+}
+
+run();
+```
+Error handling and parallelism:
+```javascript
+async function run() {
+  try {
+    let values = await Promise.all([step1(), step2()]);
+    console.log(values);
+  } catch (error) {
+    console.log(error);
+  }
+}
+```
+
+## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
+- **Promise `.then()` chaining** — explicit, but reads as nested handler functions and requires returning each step. [S1]
+- **async/await** — the same logic written like normal step-by-step code, with `try...catch` for errors; recommended for readability. Use sequential `await` for dependent steps and `Promise.all` for independent ones. [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:** 0.89
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[JavaScript Tutorial]]
+- **관련 개념:** [[JavaScript Promise]], [[JavaScript Async Fetch]], [[JavaScript Async Callbacks]], [[JavaScript Async Debug]]
+- **참조 맥락:** The syntactic sugar over promises that most modern async data-fetching code uses.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript Async Await — https://www.w3schools.com/js/js_async_await.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Async Await" page (Astra wiki-curation, P-Reinforce v3.1 format).