Memory Leak Audit

This is a checklist-driven audit for catching disposable and event listener leaks in VS Code extension code. You'd reach for it when reviewing code that registers DOM handlers, fixing reported leaks where listener counts grow unbounded, or working with lifecycle callbacks. It walks through six patterns in order: using addDisposableListener for DOM events, Event.once for one-time fires, MutableDisposable for methods called repeatedly, model-tied DisposableStores, resource pool disposal scoping, and test validation. Each rule is validated against actual VS Code PRs where these patterns prevented or fixed real leaks. The practical bit is the sequential checklist format, since missing even one pattern can leak thousands of objects over time.

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last updated: Aug 21, 2026

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Install

$ npx -y skills add microsoft/vscode --skill memory-leak-audit --agent claude-code

Installs into .claude/skills of the current project.

Files

Memory Leak Audit

The #1 bug category in VS Code. This skill encodes the patterns that prevent and fix leaks.

When to Use

Reviewing code that registers event listeners or DOM handlers
Fixing reported memory leaks (listener counts growing over time)
Creating objects in methods that are called repeatedly
Working with model lifecycle events (onWillDispose, onDidClose)
Adding event subscriptions in constructors or setup methods

Audit Checklist

Work through each check in order. A single missed pattern can cause thousands of leaked objects.

Step 1: DOM Event Listeners

Rule: Never use raw .onload, .onclick, or addEventListener() directly. Always use addDisposableListener().

// BAD — leaks a listener every call
this.iconElement.onload = () => { ... };

// GOOD — tracked and disposable
this._register(addDisposableListener(this.iconElement, 'load', () => { ... }));

Validated by: PR #280566 — Extension icon widget leaked 185 listeners after 37 toggles.