Memory Leak Debugging

This skill provides expert guidance and workflows for finding, diagnosing, and fixing memory leaks in JavaScript and Node.js applications.

Core Principles

• Prefer memlab: Do NOT attempt to read raw .heapsnapshot files directly, as they are extremely large and will consume too many tokens. Always recommend and use memlab to process snapshots and identify leak traces.
• Isolate the Leak: Determine if the leak is in the browser (client-side) or Node.js (server-side).
• Common Culprits: Look for detached DOM nodes, unhandled closures, global variables, event listeners not being removed, and caches growing unbounded. Note: Detached DOM nodes are sometimes intentional caches; always ask the user before nulling them.

Workflows

1. Capturing Snapshots

When investigating a frontend web application memory leak, utilize the chrome-devtools-mcp tools to interact with the application and take snapshots.

• Use tools like click, navigate_page, fill, etc., to manipulate the page into the desired state.
• Revert the page back to the original state after interactions to see if memory is released.
• Repeat the same user interactions 10 times to amplify the leak.
• Use take_memory_snapshot to save .heapsnapshot files to disk at baseline, target (after actions), and final (after reverting actions) states.

2. Using Memlab to Find Leaks (Recommended)

Once you have generated .heapsnapshot files using take_memory_snapshot, use memlab to automatically find memory leaks.

• Read references/memlab.md for how to use memlab to analyze the generated heapsnapshots.
• Do not read raw .heapsnapshot files using read_file or cat.

3. Identifying Common Leaks

When you have found a leak trace (e.g., via memlab output), you must identify the root cause in the code.

• Read references/common-leaks.md for examples of common memory leaks and how to fix them.

4. Fallback: Comparing Snapshots Manually

If memlab is not available, you MUST use the fallback script in the references directory to compare two .heapsnapshot files and identify the top growing objects and common leak types.

Run the script using Node.js:

node compare_snapshots.js <baseline.heapsnapshot> <target.heapsnapshot>

The script will analyze and output the top growing objects by size and highlight the 3 most common types of memory leaks (e.g., Detached DOM nodes, closures, Contexts) if they are present.