electron-heap

# Heap Snapshot Analysis Parse DevTools `.heapsnapshot` files with Node scripts in `scripts/` — no DevTools UI needed. Snapshots are one big JSON: flat `nodes`/`edges` arrays. 100MB file ≈ 1.2M nodes, parses in ~30s. ## Workflow 1. **Overview** — object counts, sizes, detached DOM, big strings: ```bash node --max-old-space-size=8192 scripts/heap-stats.js <file.heapsnapshot> ``` 2. **Pick suspects** from output (see interpretation table), then trace retention: ```bash node --max-old-space-size=8192 scripts/heap-retainers.js <file.heapsnapshot> '<name-substring>' \ [--detached] [--type=object|native|closure] [--samples=N] [--props] \ [--avoid=InspectorDOMAgent,DevToolsSession,DocumentState] [--js-only] ``` - `--avoid=...` skips retainer nodes by name substring. Re-run with known-benign anchors avoided to see what *else* retains the object. - `--js-only` finds pure-JS retention paths (no native intermediates) — distinguishes app leaks from Blink-internal retention. - `--props` dumps property edges (e.g. Error `message`, ref `current`). Both scripts require `scripts/snapshot-lib.js` (parser + reverse-edge index + BFS path-to-root). ## Interpreting results | Signal | Meaning | |---|---| | Thousands of `Error` + huge `system / StackFrameInfo`, message `react-stack-top-frame`, retained via `_debugStack` | React 19 **dev-build** owner-stack instrumentation. Not a leak; absent in prod. | | Retainer path through `blink::InspectorDOMAgent` / `DevToolsSession` | DevTools itself retains it (snapshot artifact — DevTools must be open to snapshot). Ignore; re-run with `--avoid`. | | Path through `blink::DocumentState` → form control | Blink session-history form-state keeps removed input alive. Browser-internal, bounded. | | Path through `blink::FrameSelection → SelectionEditor → Range` | Page selection/caret still points into detached tree. Released on next selection change; can force with `blur()`/`getSelection().removeAllRanges()` on unmount. | | Detached DOM with **only native** retainer paths (`--js-only` finds nothing) | Not an app JS leak. One live leaf (via parent/child member pointers) pins the whole detached tree. | | Detached DOM with a JS path (fiber `memoizedState`, module map, store, cache) | Real app leak — fix the JS retainer. | | `FiberNode` via `__reactFiber$` expando on a retained DOM node | Normal: React never deletes expandos; fiber lives as long as its DOM node. Fix the DOM retention, not the fiber. | | `PerformanceMeasure` accumulating under `blink::UserTiming` | `performance.measure()` entries never cleared (React dev tracks or app perf code). Bounded noise unless growing. | | `system / ExternalStringData` large | Script sources + big JSON strings (e.g. emoji data). Usually expected. | ## Gotchas - `edges[].to_node` is a byte offset into `nodes` — divide by node-field count (lib handles this). - Shortest retainer path ≠ only path. Kill one anchor and the next takes over — enumerate direct retainers before concluding. - Everything in a snapshot is live by definition; "leak" means *unexpected* retainer, not unreachable memory. - Skip `weak` edges when tracing (lib does). - Comparing two snapshots (before/after) beats staring at one: diff constructor counts from `heap-stats.js` runs.