Heap snapshot for memory leaks in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a heap snapshot in Node.js?

A heap snapshot is a detailed record of the memory used by a Node.js application at a specific time. It shows all objects in memory and their relationships, helping to find memory leaks.

beginner

How do you take a heap snapshot using Chrome DevTools with Node.js?

You start your Node.js app with the --inspect flag, open Chrome DevTools, connect to the Node process, go to the Memory tab, and click 'Take heap snapshot'.

intermediate

Why are heap snapshots useful for finding memory leaks?

Heap snapshots show which objects stay in memory longer than expected. By comparing snapshots over time, you can spot objects that should be gone but are still kept, indicating leaks.

intermediate

What does the 'Retainers' view in a heap snapshot show?

The 'Retainers' view shows what other objects are keeping a selected object in memory. This helps find why an object is not being removed and causing a memory leak.

beginner

Name one common cause of memory leaks visible in heap snapshots.

One common cause is forgotten event listeners or timers that keep references to objects, preventing garbage collection.

What flag do you use to enable debugging for heap snapshots in Node.js?

A --memory-check

B --debug

C --inspect

D --heap-snapshot

The --inspect flag enables the Node.js process to be debugged and connected to Chrome DevTools for heap snapshots.

Which Chrome DevTools tab do you use to take a heap snapshot?

A Console

B Memory

C Sources

D Network

The Memory tab in Chrome DevTools is used to take heap snapshots and analyze memory usage.

What does a heap snapshot NOT show?

A Retainers of objects

B References between objects

C Objects in memory

D CPU usage

Heap snapshots focus on memory, not CPU usage.

If an object is still in memory but should be gone, what might this indicate?

A A memory leak

B Garbage collection is working fine

C The app is idle

D The object is a primitive type

Objects that stay in memory unexpectedly often indicate a memory leak.

What is a common cause of memory leaks visible in heap snapshots?

A Forgotten event listeners

B Unused variables

C Fast CPU speed

D Small heap size

Forgotten event listeners keep references alive, causing memory leaks.

Explain how to take and use a heap snapshot to find memory leaks in a Node.js app.

Think about the steps from starting the app to analyzing objects in memory.

Describe what information a heap snapshot provides and why it is helpful for debugging memory issues.

Focus on what you see in the snapshot and how it helps find leaks.