2nd/10_Wiki/Topic_JavaScript/JavaScript_Assignment.md

---
id: javascript-assignment
title: "JavaScript Assignment"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["JS assignment operators", "compound assignment", "logical assignment", "falsy values", "truthy values", "nullish coalescing assignment", "spread operator"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.87
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools", "assignment", "operators"]
raw_sources: ["https://www.w3schools.com/js/js_assignment.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Assignment]]

## 🎯 한 줄 통찰 (One-line insight)
Assignment operators assign values to variables — `=` for a plain assignment and compound forms (`+=`, `-=`, `*=`, `**=`, `/=`, `%=`) plus logical forms (`&&=`, `||=`, `??=`) for assign-and-operate in one step. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Assignment operators assign values** — they assign values to JavaScript variables. [S1]
- **Compound assignment** — arithmetic compound operators combine an operation with assignment, e.g. `x += y` is the same as `x = x + y`. [S1]
- **Logical assignment** — `&&=`, `||=`, and `??=` assign conditionally based on truthiness/falsiness/nullishness. [S1]
- **8 falsy values** — `false`, `0`, `-0`, `0n`, `""` (empty strings), `null`, `undefined`, and `NaN` are falsy. [S1]
- **Truthy surprises** — `"0"`, `"false"`, `[]`, and `{}` are truthy even though they look "empty". [S1]
- **Spread `...`** — the `...` operator splits iterables into individual elements. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Mutate in place** — apply an operation to a variable and store back with one compound operator (`x += 5`). [S1]
- **Conditional assignment** — `x ??= 10` assigns only when `x` is null/undefined; `x ||= 10` when falsy; `x &&= 10` when truthy. [S1]
- **Falsy check awareness** — remember `"0"` and `"false"` strings (and `[]`/`{}`) are truthy when writing conditions. [S1]

## 📖 세부 내용 (Details)
**JavaScript Assignment Operators** [S1]
Assignment operators assign values to JavaScript variables. Using `x = 10` and `y = 5` for the examples below, the result column shows the value after applying the operator:

| Operator | Example | Same As | Result |
|----------|---------|---------|--------|
| = | x = y | x = y | x = 5 |
| += | x += y | x = x + y | x = 15 |
| -= | x -= y | x = x - y | x = 5 |
| *= | x *= y | x = x * y | x = 50 |
| **= | x **= y | x = x ** y | x = 100000 |
| /= | x /= y | x = x / y | x = 2 |
| %= | x %= y | x = x % y | x = 0 |

**The = Operator** [S1]
```javascript
let x = 10;
```

**The += Operator** [S1]
```javascript
let x = 10;
x += 5;
```

**The -= Operator** [S1]
```javascript
let x = 10;
x -= 5;
```

**The *= Operator** [S1]
```javascript
let x = 10;
x *= 5;
```

**The **= Operator** [S1]
```javascript
let x = 10;
x **= 5;
```

**The /= Operator** [S1]
```javascript
let x = 10;
x /= 5;
```

**The %= Operator** [S1]
```javascript
let x = 10;
x %= 5;
```

**Logical Assignment Operators** [S1]

The `&&=` Operator (Logical AND assignment):
```javascript
let x = true;
let y = x &&= 10;
```
The `||=` Operator (Logical OR assignment):
```javascript
let x = false;
let y = x ||= 10;
```
The `??=` Operator (Nullish Coalescing assignment):
```javascript
let x;
x ??= 10;
```

**The 8 FALSY Values** [S1]
The following values are falsy: `false`, `0`, `-0`, `0n`, `""` / `''` / `` (empty strings), `null`, `undefined`, and `NaN`.

**These are TRUTHY** [S1]
The following values are truthy: `"0"` (string), `"false"` (string), `[]` (empty array), and `{}` (empty object).

**The Spread (...) Operator** [S1]
The `...` operator splits iterables into individual elements.

## 🛠️ 적용 사례 (Applied in summary)
The page's own snippets are the canonical applied examples — each compound operator demonstrated against `let x = 10`, and the logical-assignment operators shown against boolean/undefined seeds. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Compound arithmetic assignment:
```javascript
let x = 10;
x += 5;
```
Nullish-coalescing assignment (only assigns when null/undefined):
```javascript
let x;
x ??= 10;
```
Logical OR assignment (assigns when falsy):
```javascript
let x = false;
let y = x ||= 10;
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source. Worth noting: `"0"`, `"false"`, `[]`, and `{}` are truthy despite intuition, which the source explicitly flags.

## ✅ 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:** 0.87
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Operators]], [[JavaScript Arithmetic]], [[JavaScript Comparisons]], [[JavaScript Types]]
- **참조 맥락:** Referenced whenever updating a variable's value or doing conditional/defaulting assignment.

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

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