---
id: javascript-sets
title: "JavaScript Sets"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["Set", "new Set", "unique values", "ES6 Set", "Set add", "Set collection"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools", "set", "collection", "es6"]
raw_sources: ["https://www.w3schools.com/js/js_sets.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Sets]]

## 🎯 한 줄 통찰 (One-line insight)
A JavaScript Set is a collection of unique values — each value can occur only once — built either from an array or by adding values one at a time, and iterable with `for...of`. [S1]

## 🧠 핵심 개념 (Core concepts)
- **A Set is a collection of unique values.** Each value can only occur once in a Set, and values can be of any type — primitive values or objects. [S1]
- **Two ways to create a Set** — pass an array to `new Set()`, or create an empty `new Set()` and use `add()`. [S1]
- **`add()` ignores duplicates** — adding a value that already exists has no effect; only the first occurrence is retained. [S1]
- **Sets are iterable** — a `for...of` loop lists all elements. [S1]
- **Type identity** — `typeof` a Set returns `"object"`, and `instanceof Set` returns `true`. [S1]
- **Set is an ES6 feature** with full support in all modern browsers since June 2017. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Deduplicate by construction** — feeding values into a Set automatically discards repeats. [S1]
- **Empty-then-populate** — `const s = new Set();` followed by repeated `s.add(...)`. [S1]
- **Add variables, not just literals** — `add()` accepts any value, including variables holding objects. [S1]

## 📖 세부 내용 (Details)
A JavaScript Set is a collection of unique values. Each value can only occur once in a Set. The values can be of any type, primitive values or objects. [S1]

**How to create a Set** — you can create a JavaScript Set by passing an array to `new Set()`, or create an empty Set and add values. [S1]

**The new Set() Method** — pass an array to the `new Set()` constructor: [S1]
```javascript
// Create a Set
const letters = new Set(["a","b","c"]);
```

Create an empty Set and add values with `add()`: [S1]
```javascript
// Create a Set
const letters = new Set();

// Add Values to the Set
letters.add("a");
letters.add("b");
letters.add("c");
```

You can add variables to a Set: [S1]
```javascript
// Create a Set
const letters = new Set();

// Create Variables
const a = "a";
const b = "b";
const c = "c";

// Add Variables to the Set
letters.add(a);
letters.add(b);
letters.add(c);
```

**The add() Method** [S1]
```javascript
letters.add("d");
letters.add("e");
```

If you add equal elements, only the first will be saved: [S1]
```javascript
letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
```

**Listing the Elements** — you can list all the elements of a Set with a `for...of` loop: [S1]
```javascript
// Create a Set
const letters = new Set(["a","b","c"]);

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

**A JavaScript Set is an Object** [S1]
```javascript
typeof letters;      // Returns object
```
```javascript
letters instanceof Set;  // Returns true
```

**Browser Support** — Set is an ES6 feature (JavaScript 2015), fully supported in all modern browsers since June 2017. [S1]

| Browser | Version | Release |
|---------|---------|---------|
| Chrome | 51 | May 2016 |
| Edge | 15 | Apr 2017 |
| Firefox | 54 | Jun 2017 |
| Safari | 10 | Sep 2016 |
| Opera | 38 | Jun 2016 |

## 🛠️ 적용 사례 (Applied in summary)
The page's own snippets are the canonical applied examples — building a `letters` Set from an array or by adding values, demonstrating that duplicate `add()` calls collapse to one, and listing elements with `for...of`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Create a Set from an array (language: JavaScript):
```javascript
const letters = new Set(["a","b","c"]);
```
Iterate a Set:
```javascript
let text = "";
for (const x of letters) {
  text += x;
}
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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 Set Methods]], [[JavaScript Set Logic]], [[JavaScript Maps]]
- **참조 맥락:** The base concept referenced whenever a collection of unique values is needed.

## 📚 출처 (Sources)
- [S1] W3Schools — JavaScript Sets — https://www.w3schools.com/js/js_sets.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Sets" page (Astra wiki-curation, P-Reinforce v3.1 format).
