---
id: javascript-generators
title: "JavaScript Generators"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["JS generators", "function*", "yield", "generator object", "generator function"]
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", "generators", "yield", "iterators"]
raw_sources: ["https://www.w3schools.com/js/js_generators.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Generators]]

## 🎯 한 줄 통찰 (One-line insight)
A JavaScript generator, declared with `function*`, can return multiple values one by one and can be paused and resumed using the `yield` keyword, returning a Generator Object that follows both the iterable and iterator protocols. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`function*` defines a generator** — generator functions use the `function*` syntax and, when invoked, return a Generator Object rather than a single value. [S1]
- **Returns multiple values, one by one** — a generator can return (yield) a stream of multiple values, one at a time. [S1]
- **Pausable and resumable** — generators can be paused and resumed; the `yield` keyword pauses execution and yields a value back to the caller while preserving internal state. [S1]
- **Both iterable and iterator** — Generator Objects follow both the iterable and iterator protocols, so they work with `for...of` loops. [S1]
- **`next()` shape** — calling `next()` returns an object of the form `{value: value, done: true|false}`. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Yield a sequence** — use multiple `yield` statements inside a `function*` to emit values one at a time on each `next()` call. [S1]
- **`yield` vs `return`** — `yield` produces a value and pauses; `return` ends the generator. [S1]
- **Consume with `for...of`** — because a generator is iterable, you can loop over its yielded values directly. [S1]

## 📖 세부 내용 (Details)
**JavaScript Generators**
Generators are functions that can return multiple values, one by one. A JavaScript Generator can yield a stream of data. Generators can be paused and resumed. [S1]

**Generator Functions**
Generator functions are defined with the `function*` syntax. When called, a generator function does not run its body immediately — instead it returns a Generator Object structured as `{value:1, done:false}`. [S1]

**Example — a generator with `yield` and `return`** [S1]
```javascript
function* myStream() {
  yield 1;
  yield 2;
  return 3;
}

let myGenerator = myStream();

for (let value of myGenerator) { }
```

**The `yield` Keyword**
The `yield` keyword pauses execution and yields a value back to the caller. Generators maintain their internal state between `yield` calls, enabling resumption from the previous stopping point. [S1]

**Generator Object Methods** [S1]

| Method | Description |
|--------|-------------|
| `next()` | Resumes execution of the generator function |
| `return()` | Finishes execution and returns the given value |
| `throw()` | Throws an exception in execution |

The `next()` method resumes execution of the generator function and returns `{ value: value, done: true|false}`. [S1]

**Use Cases**
Generators simplify creating custom iterators for complex data structures, enable efficient on-demand value generation including potentially infinite data streams, and historically were used to manage asynchronous operations before `async/await` became standard. [S1]

## 🛠️ 적용 사례 (Applied in summary)
The page's `myStream` generator (two `yield`s and a `return`, consumed via `for...of`) is the canonical applied example. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Define and consume a generator (language: JavaScript):
```javascript
function* myStream() {
  yield 1;
  yield 2;
  return 3;
}

let myGenerator = myStream();

for (let value of myGenerator) { }
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
The page notes that generators were historically used to manage asynchronous operations before `async/await` became the standard approach. [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:** 0.87
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Iterators]], [[JavaScript Iterables]], [[JavaScript Symbols]]
- **참조 맥락:** Referenced when building custom iterators or producing lazy/on-demand value streams.

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

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