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-string-search
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title: "JavaScript String Search"
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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: ["string search", "indexOf", "search", "match", "includes", "startsWith", "endsWith"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.90
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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", "strings", "search", "regexp"]
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raw_sources: ["https://www.w3schools.com/js/js_string_search.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[JavaScript String Search]]
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## 🎯 한 줄 통찰 (One-line insight)
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JavaScript offers eight string-search methods — `indexOf`/`lastIndexOf` return positions, `search`/`match`/`matchAll` accept regular expressions, and `includes`/`startsWith`/`endsWith` return booleans. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **`indexOf()`** — returns the index of the first occurrence of a string, or -1 if not found; positions are counted from zero. [S1]
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- **`lastIndexOf()`** — returns the index of the last occurrence; like `indexOf()` it returns -1 if not found. [S1]
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- **Second parameter = start position** — both `indexOf()` and `lastIndexOf()` accept a second parameter as the starting position; `lastIndexOf()` searches backwards from that position. [S1]
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- **`search()`** — searches for a string (or regular expression) and returns the position of the match. [S1]
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- **`indexOf()` vs `search()` are NOT equal** — `search()` cannot take a second start-position argument; `indexOf()` cannot take regular expressions. [S1]
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- **`match()`** — returns an array of matches against a string or regex; without the `g` modifier it returns only the first match. [S1]
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- **`matchAll()`** — returns an iterator of matches (ES2020); a regex parameter must set the global flag `g` or a TypeError is thrown. [S1]
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- **`includes()` / `startsWith()` / `endsWith()`** — return `true`/`false`; all are case sensitive ES6 features. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Find-or-handle-missing** — call `indexOf()` and compare to -1 to branch on presence. [S1]
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- **Search from an offset** — pass a start position to skip an earlier portion of the string. [S1]
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- **Regex matching with flags** — use `/pattern/g` for all matches and `/pattern/gi` for case-insensitive global matching. [S1]
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- **Boolean membership check** — prefer `includes()` / `startsWith()` / `endsWith()` when you only need a yes/no answer. [S1]
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## 📖 세부 내용 (Details)
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**String Search Methods**
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The page lists eight methods: `indexOf()`, `lastIndexOf()`, `search()`, `match()`, `matchAll()`, `includes()`, `startsWith()`, and `endsWith()`. [S1]
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**indexOf()** — returns the index (position) of the first occurrence of a string in a string, or -1 if not found. JavaScript counts positions from zero. [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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let index = text.indexOf("locate");
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```
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With a second parameter as the starting position: [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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let index = text.indexOf("locate", 15);
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```
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**lastIndexOf()** — returns the index of the last occurrence of a specified text. Both `indexOf()` and `lastIndexOf()` return -1 if the text is not found. [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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let index = text.lastIndexOf("locate");
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```
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Returns -1 when not found: [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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let index = text.lastIndexOf("John");
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```
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`lastIndexOf()` searches backwards (from end to beginning); if the second parameter is `15`, the search starts at position 15 and searches toward the beginning. [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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text.lastIndexOf("locate", 15);
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```
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**search()** — searches a string for a string (or a regular expression) and returns the position of the match. [S1]
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```javascript
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let text = "Please locate where 'locate' occurs!";
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text.search("locate");
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```
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```javascript
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let text = "Please locate where 'locate' occurs!";
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text.search(/locate/);
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```
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**Did You Notice?** — `indexOf()` and `search()` are NOT equal. The differences: `search()` cannot take a second start-position argument; `indexOf()` cannot take powerful search values (regular expressions). [S1]
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**match()** — returns an array containing the results of matching a string against a string (or regular expression). If a regular expression does not include the `g` modifier (global search), `match()` returns only the first match. [S1]
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```javascript
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let text = "The rain in SPAIN stays mainly in the plain";
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text.match("ain");
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```
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```javascript
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let text = "The rain in SPAIN stays mainly in the plain";
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text.match(/ain/);
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```
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```javascript
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let text = "The rain in SPAIN stays mainly in the plain";
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text.match(/ain/g);
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```
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```javascript
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let text = "The rain in SPAIN stays mainly in the plain";
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text.match(/ain/gi);
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```
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**matchAll()** — returns an iterator containing the results of matching against a string or regular expression. If the parameter is a regular expression, the global flag (`g`) must be set, otherwise a TypeError is thrown; for case-insensitive search the insensitive flag (`i`) must be set. `matchAll()` is an ES2020 feature and does not work in Internet Explorer. [S1]
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```javascript
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const iterator = text.matchAll("Cats");
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```
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```javascript
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const iterator = text.matchAll(/Cats/g);
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```
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```javascript
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const iterator = text.matchAll(/Cats/gi);
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```
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**includes()** — returns `true` if a string contains a specified value, otherwise `false`. It is case sensitive and an ES6 feature. [S1]
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.includes("world");
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```
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.includes("world", 12);
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```
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**startsWith()** — returns `true` if a string begins with a specified value, otherwise `false`; case sensitive ES6 feature. A start position can be specified. [S1]
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.startsWith("Hello");
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```
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.startsWith("world")
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```
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.startsWith("world", 5)
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```
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.startsWith("world", 6)
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```
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**endsWith()** — returns `true` if a string ends with a specified value, otherwise `false`; case sensitive ES6 feature. [S1]
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```javascript
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let text = "John Doe";
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text.endsWith("Doe");
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```
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```javascript
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let text = "Hello world, welcome to the universe.";
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text.endsWith("world", 11);
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```
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own snippets are the canonical applied examples — locating `"locate"` with `indexOf`/`lastIndexOf`/`search`, matching `"ain"` with regex flags, and boolean checks against `"Hello world, welcome to the universe."`. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Find first position (or -1):
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```javascript
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let index = text.indexOf("locate");
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```
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Global, case-insensitive regex match:
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```javascript
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text.match(/ain/gi);
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```
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Boolean membership check:
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```javascript
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text.includes("world");
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text.startsWith("Hello");
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text.endsWith("Doe");
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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- **`indexOf()` vs `search()`** — use `indexOf()` when you need a start-position argument; use `search()` when you need regular-expression power. They accept different arguments and are not interchangeable. [S1]
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- **`indexOf()` vs `includes()`** — use `indexOf()` when you need the position; use `includes()` when a boolean presence check is enough. [S1]
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- **`match()` vs `matchAll()`** — `match()` without `g` returns only the first match; `matchAll()` returns an iterator over all matches but requires the `g` flag for regex. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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`matchAll()` does not work in Internet Explorer (ES2020). 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:** 0.90
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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 Strings]], [[JavaScript String Methods]], [[JavaScript String Templates]], [[JavaScript RegExp]]
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- **참조 맥락:** Referenced whenever locating, matching, or testing for substrings within text.
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## 📚 출처 (Sources)
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- [S1] W3Schools — JavaScript String Search — https://www.w3schools.com/js/js_string_search.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript String Search" page (Astra wiki-curation, P-Reinforce v3.1 format).
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