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>
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id: javascript-function-invocation
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title: "JavaScript Function Invocation"
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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: ["calling a function", "function invocation", "invoke", "() operator", "calling vs referencing", "function call"]
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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", "functions", "invocation"]
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raw_sources: ["https://www.w3schools.com/js/js_function_invocation.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[JavaScript Function Invocation]]
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## 🎯 한 줄 통찰 (One-line insight)
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The code inside a function does not run when the function is defined — it runs when something *invokes* it, and the `()` operator is what invokes a function. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Definition vs invocation** — code inside a function is NOT executed when the function is defined; it executes when "something" invokes the function. [S1]
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- **Invoke vs call** — the term "invoke" is common because a function can be invoked without being called directly. [S1]
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- **The `()` operator invokes a function** — appending parentheses to a function name runs it. [S1]
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- **Calling vs referencing** — `sayHello` refers to the function itself (and returns the function); `sayHello()` refers to the function result (and returns the result). [S1]
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- **Store the returned value** — when a function returns a value you can store it in a variable. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Invoke with `()`** — `sayHello()` runs the body and yields its return value; omitting `()` yields the function object instead. [S1]
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- **Capture the result** — `let greeting = sayHello();` keeps the returned value for reuse. [S1]
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- **Invoke on an event** — wire a function to a UI event (e.g. `onclick="showHello()"`) so it runs on interaction. [S1]
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## 📖 세부 내용 (Details)
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**Calling a Function** — a defined function: [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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```
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The code inside a function is **NOT executed** when the function is **defined**. The code inside a function **will execute** when "something" **invokes** the function. It is common to use the term **invoke**, because a function can be invoked without being called. [S1]
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Invoke the function with `()`: [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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sayHello();
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```
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**Using the Returned Value** — when a function returns a value, you can store the value in a variable: [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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let greeting = sayHello();
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```
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Log the result: [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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console.log(sayHello());
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```
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**Displaying the Result** — invoke a function and write its result into the page: [S1]
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```javascript
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<p id="demo"></p>
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<script>
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function sayHello() {
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return "Hello World";
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}
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document.getElementById("demo").innerHTML = sayHello();
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</script>
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```
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**Calling a Function Many Times** — the same function can be invoked repeatedly: [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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let a = sayHello();
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let b = sayHello();
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let c = sayHello();
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```
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A converting function invoked with an argument: [S1]
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```javascript
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// Convert Fahrenheit to Celsius:
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function toCelsius(fahrenheit) {
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return (5/9) * (fahrenheit-32);
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}
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// Call the toCelcius() function
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let value = toCelsius(77);
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```
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**Calling vs Referencing a Function** — `() ` invokes; without it you get the function itself: [S1]
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```javascript
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function toCelsius(fahrenheit) {
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return (5/9) * (fahrenheit-32);
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}
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let value = toCelsius;
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```
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```javascript
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function sayHello() {
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return "Hello World";
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}
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let text = sayHello;
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```
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This is an important difference: `sayHello` refers to the **function itself** (it returns the function); `sayHello()` refers to the **function result** (it returns the result). The `()` operator invokes a function. [S1]
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**Functions Can Be Called from Anywhere** — define one function and invoke it from another (e.g. on a button click): [S1]
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```javascript
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function sayHello() {
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return "Hello World";
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}
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function showHello() {
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document.getElementById("demo").innerHTML = sayHello();
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}
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```
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```javascript
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<p id="demo"></p>
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<button onclick="showHello()">Click Me</button>
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<script>
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function sayHello() {
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return "Hello World";
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}
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function showHello() {
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document.getElementById("demo").innerHTML = sayHello();
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}
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</script>
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```
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**Common Mistakes** — [S1]
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- **Forgetting Parentheses `()`** — `sayHello` does not run the function; you must use `sayHello()`.
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- **Expecting Return** — some functions do not return a value.
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- **Expecting Output** — if a function returns a value, you must display it to see it.
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own snippets are the canonical applied examples — invoking `sayHello()`, capturing its return, logging it, writing it to `#demo`, calling it many times, and triggering `showHello()` from a button. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Invoke and capture the result (language: JavaScript):
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```javascript
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let greeting = sayHello();
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```
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Reference vs invoke:
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```javascript
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let text = sayHello; // the function itself
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let result = sayHello(); // the function's result
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```
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Invoke on a UI event:
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```javascript
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function showHello() {
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document.getElementById("demo").innerHTML = sayHello();
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}
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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 Functions]], [[JavaScript Function Definitions]], [[JavaScript Function Parameters]], [[JavaScript Function Returns]]
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- **참조 맥락:** Referenced whenever deciding how and when a defined function's body should actually run.
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## 📚 출처 (Sources)
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- [S1] W3Schools — JavaScript Function Invocation — https://www.w3schools.com/js/js_function_invocation.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Function Invocation" page (Astra wiki-curation, P-Reinforce v3.1 format).
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