2nd/10_Wiki/Topic_JavaScript/JavaScript_Control_Flow.md

---
id: javascript-control-flow
title: "JavaScript Control Flow"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["control flow", "program flow", "execution order", "JS control flow", "conditional flow"]
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", "control-flow", "loops", "conditions"]
raw_sources: ["https://www.w3schools.com/js/js_control_flow.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Control Flow]]

## 🎯 한 줄 통찰 (One-line insight)
Control flow is the order in which statements are executed; by default JavaScript runs top-to-bottom and left-to-right on a single thread, and conditions, loops, jumps, and functions are how you alter that order. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Control flow = order of execution** — control flow is the order in which statements are executed in a program. [S1]
- **Default flow is sequential** — by default JavaScript executes code sequentially from top to bottom and left to right. [S1]
- **Conditional flow** — conditions allow decision-making using `if`, `if...else`, `switch`, and the ternary (`? :`) operators. [S1]
- **Loops repeat code** — loops enable code to run multiple times using `for`, `while`, or `do...while` structures. [S1]
- **Jump statements alter flow abruptly** — using `break`, `continue`, `return`, and `throw`. [S1]
- **Functions are callable, reusable blocks** — functions run when they are called. [S1]
- **Single-threaded** — JavaScript runs on a single thread; it can only do one thing at a time, so every task waits for the completion of previous tasks. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Branch on a condition** — assign a default value, then override it inside `if/else` based on a test (e.g. `age >= 18`). [S1]
- **Repeat with a counted loop** — drive repetition with a `for` loop counter and accumulate output. [S1]
- **Early exit from a loop** — combine a loop with a `break` inside an `if` to stop early. [S1]
- **Encapsulate logic in a function** — wrap reusable computation in a function that returns a value. [S1]

## 📖 세부 내용 (Details)
**JavaScript Control Flow**
Control flow is the order in which statements are executed in a program. By default, JavaScript executes code sequentially from top to bottom and left to right. Control flow statements enable developers to alter this sequence based on conditions, loops, or keywords. [S1]

**Default Flow**
Default flow runs code sequentially from top to bottom and left to right. [S1]
```javascript
let x = 5;
let y = 6;
let z = x + y;
```

**Conditional Control Flow**
Conditions allow decision-making using `if`, `if...else`, `switch`, and ternary (`? :`) operators. [S1]
```javascript
let text = "Unknown";

if (age >= 18) {
  text = "Adult";
} else {
  text = "Minor";
}
```

**Loops (Repetition Control Flow)**
Loops enable code to run multiple times using `for`, `while`, or `do...while` structures. [S1]
```javascript
for (let i = 0; i < 5; i++) {
  text += "The number is " + i + "<br>";
}
```

**Jump Statements**
Jump statements alter flow abruptly using `break`, `continue`, `return`, and `throw`. [S1]
```javascript
for (let i = 0; i < 10; i++) {
  if (i === 3) { break; }
  text += "The number is " + i + "<br>";
}
```

**Function Flow**
Functions are callable and reusable code blocks. Functions will run when they are called. [S1]
```javascript
function myFunction(p1, p2) {
  return p1 * p2;
}
```

**JavaScript Is Single-Threaded**
JavaScript runs on a single thread. It can only do one thing at a time. Every task must wait for completion of previous tasks, potentially freezing applications during slow operations. Asynchronous programming is covered in the advanced section. [S1]

## 🛠️ 적용 사례 (Applied in summary)
The page's own snippets are the canonical applied examples — sequential assignment, an `if/else` age check, a counted `for` loop, an early `break`, and a multiplying function. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Conditional branch:
```javascript
if (age >= 18) {
  text = "Adult";
} else {
  text = "Minor";
}
```
Counted loop with early exit:
```javascript
for (let i = 0; i < 10; i++) {
  if (i === 3) { break; }
  text += "The number is " + i + "<br>";
}
```
Reusable function:
```javascript
function myFunction(p1, p2) {
  return p1 * p2;
}
```

## ⚖️ 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:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript If Else]], [[JavaScript Switch]], [[JavaScript For Loop]], [[JavaScript Break]], [[JavaScript Continue]], [[JavaScript Functions]]
- **참조 맥락:** The conceptual umbrella for every statement that changes execution order in a JavaScript program.

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

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