npx skills add ...
npx skills add microsoft/vscode --skill memory-leak-audit
npx skills add microsoft/vscode --skill memory-leak-audit
Audit code for memory leaks and disposable issues. Use when reviewing event listeners, DOM handlers, lifecycle callbacks, or fixing leak reports. Covers addDisposableListener, Event.once, MutableDisposable, DisposableStore, and onWillDispose patterns.
The #1 bug category in VS Code. This skill encodes the patterns that prevent and fix leaks.
Work through each check in order. A single missed pattern can cause thousands of leaked objects.
Rule: Never use raw .onload, .onclick, or addEventListener() directly. Always use addDisposableListener().
Validated by: PR #280566 — Extension icon widget leaked 185 listeners after 37 toggles.
Rule: Use Event.once() for events that should only fire once (lifecycle events, close events, first-change events).
Validated by: PRs #285657, #285661 — Terminal lifecycle hacks replaced with Event.once().
Rule: Objects created in methods called multiple times must NOT be registered to the class this._register(). Use MutableDisposable or return IDisposable to the caller.
When the event should only fire once per method call, combine Event.once() with MutableDisposable — this auto-removes the listener after the first invocation while still guarding against repeated calls:
Validated by: PR #283466 — Terminal find widget leaked 1 listener per search.
Rule: When creating a DisposableStore tied to a model's lifetime, register model.onWillDispose(() => store.dispose()) to the store itself.
Validated by: Pattern used in chatEditingSession.ts, fileBasedRecommendations.ts, testingContentProvider.ts.
Rule: When using factory methods that create pooled objects (lists, trees), disposables must be registered to the individual item, not the pool class.
Validated by: PR #290505 — Chat content parts CollapsibleListPool and TreePool leaked disposables.
Rule: Every test suite that creates disposable objects must call ensureNoDisposablesAreLeakedInTestSuite().
| Scenario | Pattern | Anti-Pattern |
|---|---|---|
| DOM events | addDisposableListener() | .onclick =, addEventListener() |
| One-time events | Event.once(event)(handler) | event(handler) for lifecycle |
| Repeated methods | MutableDisposable or return IDisposable | this._register() in non-constructor |
| Model lifecycle | store.add(model.onWillDispose(...)) | Forgetting cleanup |
| Pooled objects | Item-scoped DisposableStore | Pool-scoped this._register() |
| Tests | ensureNoDisposablesAreLeakedInTestSuite() | No leak checking |
After fixing leaks, verify by:
ensureNoDisposablesAreLeakedInTestSuite() in testsnpm run perf:chat-leak (see the chat-perf skill). It sends N messages in a single session, forces GC between each, and uses linear regression on heap/DOM samples to detect per-message growth. A slope above 2 MB/msg indicates a leak. Use --messages 20 --verbose for more accurate results.// BAD — listener stays registered forever after first fire
model.onDidDispose(() => store.dispose());
// GOOD — auto-removes after first invocation
Event.once(model.onDidDispose)(() => store.dispose());// BAD — every call adds another listener to the class store
startSearch() {
this._register(this.model.onResults(() => { ... }));
}
// GOOD — MutableDisposable ensures max 1 listener
private readonly _searchListener = this._register(new MutableDisposable());
startSearch() {
this._searchListener.value = this.model.onResults(() => { ... });
}private readonly _searchListener = this._register(new MutableDisposable());
startSearch() {
this._searchListener.value = Event.once(this.model.onResults)(() => { ... });
}const store = new DisposableStore();
store.add(model.onWillDispose(() => store.dispose()));
store.add(model.onDidChange(() => { ... }));// BAD — registers to pool, never cleaned per item
createItem() {
const item = new Item();
this._register(item.onEvent(() => { ... }));
return item;
}
// GOOD — wrap with item-scoped disposal
createItem(): IDisposable & Item {
const store = new DisposableStore();
const item = new Item();
store.add(item.onEvent(() => { ... }));
return { ...item, dispose: () => store.dispose() };
}import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../base/test/common/utils.js';
suite('MyFeature', () => {
ensureNoDisposablesAreLeakedInTestSuite();
test('does something', () => {
// test disposables are tracked automatically
});
});