2nd/10_Wiki/Topics/Topic_Programming/Topic_JavaScript/JavaScript_Async.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
javascript-async	JavaScript Async	Frontend	draft	conceptual		Async programming JS async basics Synchronous vs asynchronous Async execution order Non-blocking code		B	0.87	2026-06-23	2026-06-23			javascript js web frontend w3schools asynchronous settimeout	https://www.w3schools.com/js/js_async.asp

JavaScript Async

🎯 한 줄 통찰 (One-line insight)

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]

🧠 핵심 개념 (Core concepts)

• Default execution is top-to-bottom, left-to-right — JavaScript normally executes one line at a time in source order. [S1]
• 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]
• The result-not-ready problem — reading an async result too early yields undefined because the async code has not finished yet. [S1]
• 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]
• Six building blocks — synchronous flow, timers, callbacks, events, promises, and async/await. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Order swap by call order — calling mySecond() before myFirst() simply changes which output appears first; ordinary synchronous calls obey source order. [S1]
• Deferred call via setTimeout — wrapping a call in setTimeout(fn, ms) pushes it after the synchronous lines, yielding A, C, B. [S1]
• Event-driven callback — an HTML attribute like onclick wires user interaction to a function that runs later. [S1]

📖 세부 내용 (Details)

Synchronous calls run in order Plain calls produce output A, B, C: [S1]

myDisplayer("A");
myDisplayer("B");
myDisplayer("C");

Function order matters Defining two functions and calling them in order: [S1]

function myFirst() {
  myDisplayer("Hello");
}

function mySecond() {
  myDisplayer("Goodbye");
}

myFirst();
mySecond();

Swapping the call order swaps the output: [S1]

function myFirst() {
  myDisplayer("Hello");
}

function mySecond() {
  myDisplayer("Goodbye");
}

mySecond();
myFirst();

Asynchronous flow with setTimeout The deferred B runs after the synchronous C, so the order is A, C, B: [S1]

myDisplayer("A");

setTimeout(function() {
  myDisplayer("B");
}, 1000);

myDisplayer("C");

The result-not-ready trap The result is undefined because the async code has not finished yet: [S1]

let result;

setTimeout(function() {
  result = 5;
}, 1000);

// What is result here?

JavaScript events Events wire callbacks to user interaction: [S1]

<button onclick="displayDate()">The time is?</button>

Core async concepts [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'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.

💻 코드 패턴 (Code patterns)

Deferred execution that reorders output (language: JavaScript):

myDisplayer("A");

setTimeout(function() {
  myDisplayer("B");
}, 1000);

myDisplayer("C");

Event-driven callback:

<button onclick="displayDate()">The time is?</button>

⚖️ 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: 0.87
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: JavaScript Tutorial
• 관련 개념: JavaScript Asynchronous, JavaScript Async Timeouts, JavaScript Async Callbacks, JavaScript Promise
• 참조 맥락: The foundational lesson establishing why execution order matters before introducing timeouts, callbacks, and promises.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Async — https://www.w3schools.com/js/js_async.asp

📝 변경 이력 (Change history)

• 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Async" page (Astra wiki-curation, P-Reinforce v3.1 format).