2nd/10_Wiki/Topics/Frontend/Memory-Leak-Debugging-in-JavaScript.md

---
id: wiki-2026-0508-memory-leak-debugging-in-javascr
title: Memory Leak Debugging in JavaScript
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [JS Memory Leak, Heap Leak Debugging]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [javascript, performance, debugging, memory]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript
  framework: Chrome DevTools
---

# Memory Leak Debugging in JavaScript

## 매 한 줄
> **"매 unintended retention — 매 GC 매 reach 가능한 reference chain 매 끊지 못해 매 heap 매 grows unbounded"**. JS 매 mark-and-sweep GC 자동이지만 매 closure/listener/global/timer 매 long-lived reference 매 object lifecycle 매 의도와 분리시키면 매 leak 발생, 매 Chrome DevTools Heap Snapshot 매 진단 standard.

## 매 핵심

### 매 leak sources (top 5)
- **Detached DOM nodes**: 매 element removed from tree 매 JS reference 잔존.
- **Event listeners**: 매 addEventListener 매 removeEventListener 없이 매 component unmount.
- **Timers**: setInterval/setTimeout 매 cleanup 누락 매 closure 매 모두 retain.
- **Closures**: outer scope variables 매 inner function 매 capture 후 매 long-lived.
- **Global accumulation**: window/globalThis 매 cache/array 매 unbounded push.

### 매 detection tools
- **Chrome DevTools Memory**: Heap snapshot, allocation timeline, allocation sampling.
- **performance.measureUserAgentSpecificMemory()** (Chrome 89+): 매 cross-origin isolated context.
- **Node.js**: --inspect + Chrome DevTools, heapdump module, --heap-prof flag.
- **WeakRef + FinalizationRegistry**: 매 GC 관찰 (debugging only).

### 매 응용
1. SPA 매 route navigation 매 retain leak 진단.
2. Long-running dashboard 매 hour-scale leak 감시.
3. Node.js server 매 RSS growth 매 root cause.
4. React/Vue component lifecycle leak detection.

## 💻 패턴

### Heap snapshot 3-snapshot technique
```
1. App 초기 load → Snapshot 1 (baseline)
2. Suspect action 수행 (modal open/close ×10) → Snapshot 2
3. 동일 action 재수행 → Snapshot 3
4. Snapshot 3 의 Comparison → Snapshot 1
5. "Allocated between snapshots 1 and 3" 의 still-alive objects = leak
```

### Detached DOM 탐색 (DevTools Console)
```js
// Heap snapshot Class filter:
//   "Detached HTMLDivElement"
//   "Detached HTMLElement"
// 매 instance 매 retainer chain 매 inspect — 매 root retainer 매 leak 출처
```

### Event listener leak — fix pattern
```js
// 매 BAD
class Widget {
  constructor() {
    window.addEventListener('resize', this.onResize.bind(this));
  }
  onResize() { /* ... */ }
  destroy() { /* listener still attached */ }
}

// 매 GOOD
class Widget {
  constructor() {
    this.onResize = this.onResize.bind(this);
    window.addEventListener('resize', this.onResize);
  }
  onResize() { /* ... */ }
  destroy() {
    window.removeEventListener('resize', this.onResize);
  }
}
```

### AbortController 매 modern cleanup
```js
class Component {
  constructor() {
    this.ac = new AbortController();
    const { signal } = this.ac;
    window.addEventListener('scroll', this.onScroll, { signal });
    window.addEventListener('resize', this.onResize, { signal });
    fetch('/api', { signal });
  }
  destroy() {
    this.ac.abort(); // 매 모든 listener + fetch 매 한 번에 cleanup
  }
}
```

### Timer leak fix
```js
// 매 BAD — closure captures large data
function startPolling(bigData) {
  setInterval(() => {
    console.log(bigData.length); // bigData retained forever
  }, 1000);
}

// 매 GOOD — explicit handle + cleanup
const handle = setInterval(poll, 1000);
function stop() { clearInterval(handle); }
```

### WeakMap 매 cache without leak
```js
// 매 BAD — Map 매 key 매 GC X
const cache = new Map();
function getMeta(node) {
  if (!cache.has(node)) cache.set(node, computeMeta(node));
  return cache.get(node); // node removed from DOM but still in cache
}

// 매 GOOD — WeakMap key 매 GC 가능
const cache = new WeakMap();
function getMeta(node) {
  if (!cache.has(node)) cache.set(node, computeMeta(node));
  return cache.get(node);
}
```

### performance.measureUserAgentSpecificMemory
```js
// crossOriginIsolated context (COOP+COEP headers) 필요
if (crossOriginIsolated && performance.measureUserAgentSpecificMemory) {
  const result = await performance.measureUserAgentSpecificMemory();
  console.log('bytes:', result.bytes);
  console.table(result.breakdown);
}
```

### FinalizationRegistry 매 GC 관찰 (debug only)
```js
const registry = new FinalizationRegistry((tag) => {
  console.log(`GC'd: ${tag}`);
});

class Tracked {
  constructor(name) {
    registry.register(this, name);
  }
}

new Tracked('widget-1'); // → "GC'd: widget-1" eventually (or never)
```

### Node.js heap snapshot
```bash
node --inspect server.js
# 매 chrome://inspect → Memory → Take heap snapshot
# 또는 programmatic:
```
```js
import { writeHeapSnapshot } from 'node:v8';
const path = writeHeapSnapshot(); // .heapsnapshot file
console.log(`Snapshot: ${path}`);
```

## 매 결정 기준
| 상황 | Tool/Approach |
|---|---|
| Browser SPA growing memory | DevTools Heap Snapshot 3-snapshot |
| 매 frame allocation hotspot | Allocation timeline (sampling) |
| Detached DOM 의심 | Class filter "Detached " in snapshot |
| Node.js RSS growth | writeHeapSnapshot + Chrome DevTools |
| Continuous monitoring (production) | performance.measureUserAgentSpecificMemory |
| Event listener leak | AbortController 매 unified cleanup |

**기본값**: 매 Heap Snapshot 3-snapshot diff — 매 retainer chain 매 따라 root 매 식별.

## 🔗 Graph
- 부모: [[JavaScript-Performance]] · [[Garbage-Collection]]
- 변형: [[Node-js-Memory-Profiling]] · [[V8-Heap-Analysis]]
- 응용: [[SPA-Performance]] · [[Long-Running-Apps]]
- Adjacent: [[Chrome-DevTools]] · [[WeakMap]] · [[AbortController]] · [[FinalizationRegistry]]

## 🤖 LLM 활용
**언제**: 매 SPA/long-running app 의 메모리 증가, 매 unmount 후 referent 잔존, 매 production memory metrics 의 anomaly.
**언제 X**: 매 short-lived script (CLI tool), 매 GC pause 문제 (different — GC tuning territory).

## ❌ 안티패턴
- **`delete` keyword 의존**: 매 reference 매 nullify 안 함 — 매 다른 reference 매 retain.
- **`window.gc()` 매 production**: 매 only with --expose-gc flag, 매 hint 일 뿐.
- **Allocation timeline 매 production trace**: 매 overhead 매 큼 — 매 staging 에서.
- **One-snapshot 진단**: 매 baseline 없으면 매 noise 와 leak 매 구분 불가.
- **DevTools 매 incognito 가정**: 매 extension 매 heap pollution — 매 incognito + 매 disabled extensions.

## 🧪 검증 / 중복
- Verified (Chrome DevTools docs, V8 blog, Node.js v8 module).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — leak source taxonomy + DevTools workflow + AbortController/WeakMap patterns |