2nd/10_Wiki/Topic_JavaScript/JavaScript_Set_Methods.md

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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-set-methods	JavaScript Set Methods	Frontend	draft	conceptual		Set methods Set.add Set.has Set.size Set.values Set.entries Set.forEach		B	0.9	2026-06-23	2026-06-23			javascript js web frontend w3schools set methods	https://www.w3schools.com/js/js_set_methods.asp

JavaScript Set Methods

🎯 한 줄 통찰 (One-line insight)

The core Set methods — add, delete, clear, has, forEach, values, keys, entries, plus the size property — manage and iterate a unique-value collection; because a Set has no keys, keys() and entries() mirror values() to stay compatible with Maps. [S1]

🧠 핵심 개념 (Core concepts)

• Sets only store unique values — if you add an element that already exists, add() has no effect and the Set is unchanged. [S1]
• size is a property, not a method — it returns the number of elements. [S1]
• has() tests membership — returns true if a value exists in the Set. [S1]
• forEach() runs a callback per element. [S1]
• values() returns an Iterator of the Set's values. [S1]
• A Set has no keys — so keys() returns the same as values(), and entries() returns [value,value] pairs. This makes Sets compatible with Maps. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Iterator-then-loop — capture letters.values() (or keys()/entries()) into a variable, then for...of it; or loop the call directly. [S1]
• Membership guard — letters.has(x) before acting on a value. [S1]
• forEach for side effects — accumulate or process each value via a callback. [S1]

📖 세부 내용 (Details)

The new Set() Method — pass an array to the new Set() constructor: [S1]

// Create a new Set
const letters = new Set(["a","b","c"]);

The add() Method [S1]

letters.add("d");
letters.add("e");

Sets only store unique values. If an attempt is made to add an element that already exists in the Set, the add() method will have no effect, and the Set will remain unchanged: [S1]

letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");

The size Property — returns the number of elements: [S1]

// Create a new Set
const mySet = new Set(["a","b","c"]);

// The number of elements are
mySet.size;

Listing Set Elements — list all elements with a for...of loop: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// List all Elements
let text = "";
for (const x of letters) {
  text += x;
}

The has() Method — returns true if a value exists: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// Does the Set contain "d"?
answer = letters.has("d");

The forEach() Method — invokes a callback for each element: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// List all entries
let text = "";
letters.forEach (function(value) {
  text += value;
})

The values() Method — returns an Iterator with the values in a Set: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// Get all Values
const myIterator = letters.values();

// List all Values
let text = "";
for (const entry of myIterator) {
  text += entry;
}

// Create a Set
const letters = new Set(["a","b","c"]);

// List all Values
let text = "";
for (const entry of letters.values()) {
  text += entry;
}

The keys() Method — a Set has no keys, so keys() returns the same as values(). This makes Sets compatible with Maps: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// Create an Iterator
const myIterator = letters.keys();

// List all Elements
let text = "";
for (const x of myIterator) {
  text += x;
}

// Create a Set
const letters = new Set(["a","b","c"]);

// List all Elements
let text = "";
for (const x of letters.keys()) {
  text += x;
}

The entries() Method — a Set has no keys, so the entries() method returns [value,value]. This makes Sets compatible with Maps: [S1]

// Create a Set
const letters = new Set(["a","b","c"]);

// Get all Entries
const myIterator = letters.entries();

// List all Entries
let text = "";
for (const entry of myIterator) {
  text += entry;
}

// Create a Set
const letters = new Set(["a","b","c"]);

// List all Entries
let text = "";
for (const entry of letters.entries()) {
  text += entry;
}

Set Methods and Properties [S1]

Method/Property	Description
new Set()	Creates a new Set
add()	Adds a new element to the Set
clear()	Removes all elements from a Set
delete()	Removes a specified element from a Set
entries()	Returns an Iterator with [value,value] pairs from a Set
forEach()	Invokes a callback for each element in the Set
has()	Returns true if a value exists in the Set
keys()	Returns an Iterator with the values in a Set
values()	Returns an Iterator with the values in a Set
size	Returns the number of elements in a Set

🛠️ 적용 사례 (Applied in summary)

The page's own snippets are the canonical applied examples — building a letters/mySet Set, reading size, testing membership with has(), and walking the Set with forEach(), values(), keys(), and entries(). No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Membership test (language: JavaScript):

answer = letters.has("d");

Iterate values via the values() iterator:

let text = "";
for (const entry of letters.values()) {
  text += entry;
}

⚖️ 모순 및 업데이트 (Contradictions & updates)

No contradictions found in the source. Note the intentional design choice: keys() and entries() echo values() because Sets have no keys — done deliberately for Map compatibility, not a bug. [S1]

✅ 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 Sets, JavaScript Set Logic, JavaScript Map Methods
• 참조 맥락: Referenced whenever managing or iterating the contents of a Set.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Set Methods — https://www.w3schools.com/js/js_set_methods.asp

📝 변경 이력 (Change history)

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