2nd/10_Wiki/Topic_JavaScript/JavaScript_String_Search.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-string-search	JavaScript String Search	Frontend	draft	conceptual		string search indexOf search match includes startsWith endsWith		B	0.90	2026-06-23	2026-06-23			javascript js web frontend w3schools strings search regexp	https://www.w3schools.com/js/js_string_search.asp

JavaScript String Search

🎯 한 줄 통찰 (One-line insight)

JavaScript offers eight string-search methods — indexOf/lastIndexOf return positions, search/match/matchAll accept regular expressions, and includes/startsWith/endsWith return booleans. [S1]

🧠 핵심 개념 (Core concepts)

• indexOf() — returns the index of the first occurrence of a string, or -1 if not found; positions are counted from zero. [S1]
• lastIndexOf() — returns the index of the last occurrence; like indexOf() it returns -1 if not found. [S1]
• Second parameter = start position — both indexOf() and lastIndexOf() accept a second parameter as the starting position; lastIndexOf() searches backwards from that position. [S1]
• search() — searches for a string (or regular expression) and returns the position of the match. [S1]
• indexOf() vs search() are NOT equal — search() cannot take a second start-position argument; indexOf() cannot take regular expressions. [S1]
• match() — returns an array of matches against a string or regex; without the g modifier it returns only the first match. [S1]
• matchAll() — returns an iterator of matches (ES2020); a regex parameter must set the global flag g or a TypeError is thrown. [S1]
• includes() / startsWith() / endsWith() — return true/false; all are case sensitive ES6 features. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Find-or-handle-missing — call indexOf() and compare to -1 to branch on presence. [S1]
• Search from an offset — pass a start position to skip an earlier portion of the string. [S1]
• Regex matching with flags — use /pattern/g for all matches and /pattern/gi for case-insensitive global matching. [S1]
• Boolean membership check — prefer includes() / startsWith() / endsWith() when you only need a yes/no answer. [S1]

📖 세부 내용 (Details)

String Search Methods The page lists eight methods: indexOf(), lastIndexOf(), search(), match(), matchAll(), includes(), startsWith(), and endsWith(). [S1]

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]

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate");

With a second parameter as the starting position: [S1]

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate", 15);

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]

let text = "Please locate where 'locate' occurs!";
let index = text.lastIndexOf("locate");

Returns -1 when not found: [S1]

let text = "Please locate where 'locate' occurs!";
let index = text.lastIndexOf("John");

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]

let text = "Please locate where 'locate' occurs!";
text.lastIndexOf("locate", 15);

search() — searches a string for a string (or a regular expression) and returns the position of the match. [S1]

let text = "Please locate where 'locate' occurs!";
text.search("locate");

let text = "Please locate where 'locate' occurs!";
text.search(/locate/);

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]

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]

let text = "The rain in SPAIN stays mainly in the plain";
text.match("ain");

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/);

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/g);

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/gi);

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]

const iterator = text.matchAll("Cats");

const iterator = text.matchAll(/Cats/g);

const iterator = text.matchAll(/Cats/gi);

includes() — returns true if a string contains a specified value, otherwise false. It is case sensitive and an ES6 feature. [S1]

let text = "Hello world, welcome to the universe.";
text.includes("world");

let text = "Hello world, welcome to the universe.";
text.includes("world", 12);

startsWith() — returns true if a string begins with a specified value, otherwise false; case sensitive ES6 feature. A start position can be specified. [S1]

let text = "Hello world, welcome to the universe.";
text.startsWith("Hello");

let text = "Hello world, welcome to the universe.";
text.startsWith("world")

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 5)

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 6)

endsWith() — returns true if a string ends with a specified value, otherwise false; case sensitive ES6 feature. [S1]

let text = "John Doe";
text.endsWith("Doe");

let text = "Hello world, welcome to the universe.";
text.endsWith("world", 11);

🛠️ 적용 사례 (Applied in summary)

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.

💻 코드 패턴 (Code patterns)

Find first position (or -1):

let index = text.indexOf("locate");

Global, case-insensitive regex match:

text.match(/ain/gi);

Boolean membership check:

text.includes("world");
text.startsWith("Hello");
text.endsWith("Doe");

⚖️ 비교 및 선택 기준 (Comparison & decision criteria)

• 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]
• indexOf() vs includes() — use indexOf() when you need the position; use includes() when a boolean presence check is enough. [S1]
• 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]

⚖️ 모순 및 업데이트 (Contradictions & updates)

matchAll() does not work in Internet Explorer (ES2020). 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: 0.90
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: JavaScript Tutorial
• 관련 개념: JavaScript Strings, JavaScript String Methods, JavaScript String Templates, JavaScript RegExp
• 참조 맥락: Referenced whenever locating, matching, or testing for substrings within text.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript String Search — https://www.w3schools.com/js/js_string_search.asp

📝 변경 이력 (Change history)

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