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-string-methods
+title: "JavaScript String Methods"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["string methods", "slice", "substring", "trim", "replace", "split", "padStart"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.88
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["javascript", "js", "web", "frontend", "w3schools", "strings", "string-methods", "immutability"]
+raw_sources: ["https://www.w3schools.com/js/js_string_methods.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[JavaScript String Methods]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Strings are immutable, so every string method produces a new string without altering the original — covering extraction (`slice`, `substring`, `substr`), character access (`charAt`, `at`, `[]`), case, trimming, padding, and replacement. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Immutability** — all string methods produce a new string without altering the original string; strings cannot be changed, only replaced. [S1]
+- **`length`** — the `length` property returns the length of a string. [S1]
+- **Character extraction** — four ways to get a character: `at()`, `charAt()`, `charCodeAt()`, and bracket notation `[]`; `codePointAt()` returns a code point. [S1]
+- **`at()` allows negative indexes** — introduced in ES2022, `at()` allows negative indexes while `charAt()` does not. [S1]
+- **Substring extraction** — `slice()`, `substring()`, and `substr()` extract parts of a string; `substr()` is deprecated. [S1]
+- **`replace()` vs `replaceAll()`** — `replace()` replaces only the first match and is case sensitive by default; `replaceAll()` (ES2021) replaces all matches. [S1]
+- **`split()`** — converts a string into an array using a chosen delimiter. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Extract a slice by index range** — `text.slice(start, end)` (or `substring`) to pull a labeled portion. [S1]
+- **Normalize input** — chain `trim()` / `trimStart()` / `trimEnd()` then case methods to clean user input. [S1]
+- **Pad to a fixed width** — `padStart(len, "0")` to left-pad values such as IDs or amounts. [S1]
+- **Replace all occurrences** — `replaceAll(a, b)`, or `replace()` with a `/g` regex flag, since plain `replace()` only hits the first match. [S1]
+
+## 📖 세부 내용 (Details)
+> Note: All string methods produce a new string without altering the original string. Strings are immutable: strings cannot be changed, only replaced. [S1]
+
+**Length** [S1]
+```javascript
+let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+let length = text.length;
+```
+
+**charAt()** — returns the character at a given index. [S1]
+```javascript
+let text = "HELLO WORLD";
+let char = text.charAt(0);
+```
+
+**charCodeAt()** — returns the UTF-16 code of the character at a given index. [S1]
+```javascript
+let text = "HELLO WORLD";
+let char = text.charCodeAt(0);
+```
+
+**codePointAt()** — returns the Unicode code point at a given index. [S1]
+```javascript
+let text = "HELLO WORLD";
+let code = text.codePointAt(0);
+```
+
+**at()** — introduced in ES2022; allows negative indexes while `charAt()` does not. [S1]
+```javascript
+const name = "W3Schools";
+let letter = name.at(2);
+```
+
+**Property access []** — bracket notation reads a character by index. [S1]
+```javascript
+let text = "HELLO WORLD";
+let char = text[0];
+```
+
+**concat()** — joins two or more strings. [S1]
+```javascript
+let text1 = "Hello";
+let text2 = "World";
+let text3 = text1.concat(" ", text2);
+```
+
+**slice()** — extracts a part of a string between start and end positions. [S1]
+```javascript
+let text = "Apple, Banana, Kiwi";
+let part = text.slice(7, 13);
+```
+
+**substring()** — similar to `slice()`. [S1]
+```javascript
+let str = "Apple, Banana, Kiwi";
+let part = str.substring(7, 13);
+```
+
+**substr()** — deprecated; second parameter is the length to extract. [S1]
+```javascript
+let str = "Apple, Banana, Kiwi";
+let part = str.substr(7, 6);
+```
+
+**toUpperCase()** [S1]
+```javascript
+let text1 = "Hello World!";
+let text2 = text1.toUpperCase();
+```
+
+**toLowerCase()** [S1]
+```javascript
+let text1 = "Hello World!";
+let text2 = text1.toLowerCase();
+```
+
+**trim()** — removes whitespace from both sides. [S1]
+```javascript
+let text1 = "      Hello World!      ";
+let text2 = text1.trim();
+```
+
+**trimStart()** — removes whitespace from the start. [S1]
+```javascript
+let text1 = "     Hello World!     ";
+let text2 = text1.trimStart();
+```
+
+**trimEnd()** — removes whitespace from the end. [S1]
+```javascript
+let text1 = "     Hello World!     ";
+let text2 = text1.trimEnd();
+```
+
+**padStart()** — pads from the start to a given length (ES2017). [S1]
+```javascript
+let text = "5";
+let padded = text.padStart(4,"0");
+```
+
+**padEnd()** — pads from the end to a given length (ES2017). [S1]
+```javascript
+let text = "5";
+let padded = text.padEnd(4,"0");
+```
+
+**repeat()** — returns a new string with a number of copies. [S1]
+```javascript
+let text = "Hello world!";
+let result = text.repeat(2);
+```
+
+**replace()** — the `replace()` method replaces only the first match. By default, the `replace()` method is case sensitive. [S1]
+```javascript
+let text = "Please visit Microsoft!";
+let newText = text.replace("Microsoft", "W3Schools");
+```
+
+**replaceAll()** — replaces all matches (ES2021); use a `/g` flag to replace all matches with regular expressions. [S1]
+```javascript
+text = text.replaceAll("Cats","Dogs");
+text = text.replaceAll("cats","dogs");
+```
+
+**split()** — converts a string into an array using a delimiter. [S1]
+```javascript
+text.split(",")    // Split on commas
+text.split(" ")    // Split on spaces
+text.split("|")    // Split on pipe
+```
+
+Other methods listed by the page include `isWellFormed()` and `toWellFormed()`. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's own snippets are the canonical applied examples — extracting substrings from `"Apple, Banana, Kiwi"`, padding `"5"` to width 4, replacing `"Microsoft"` with `"W3Schools"`, and splitting on delimiters. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Extract a portion:
+```javascript
+let part = text.slice(7, 13);
+```
+Pad to fixed width:
+```javascript
+let padded = text.padStart(4,"0");
+```
+Replace every occurrence:
+```javascript
+text = text.replaceAll("Cats","Dogs");
+```
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+`substr()` is noted as deprecated; prefer `slice()` or `substring()`. No other 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:** 0.88
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[JavaScript Tutorial]]
+- **관련 개념:** [[JavaScript Strings]], [[JavaScript String Search]], [[JavaScript String Templates]], [[JavaScript Arrays]]
+- **참조 맥락:** Referenced whenever transforming, slicing, cleaning, or replacing text values.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — JavaScript String Methods — https://www.w3schools.com/js/js_string_methods.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript String Methods" page (Astra wiki-curation, P-Reinforce v3.1 format).