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JS Memory Leak School

Automated leak testing

memlab (browser)

Section titled “memlab (browser)”

Meta’s tool for scenario-based leak detection.

Terminal window
npx memlab run --scenario ./scenarios/open-modal.js

Defines: navigate → interact → back → repeat → analyze heap diff.

Node soak in CI

Section titled “Node soak in CI”
# sketch — run leak script with memory ceiling
- name: memory soak
  run: |
    timeout 120 node examples/node/01-global-array-fixed.js &
    PID=$!
    sleep 90
    RSS=$(ps -o rss= -p $PID | tr -d ' ')
    kill $PID
    test "$RSS" -lt 300000  # KB threshold

Fail CI if fixed script regresses.

Snapshot diff scripts

Section titled “Snapshot diff scripts”

Take heap snapshots at start/end of test suite; compare retained constructors (heavy — usually nightly job).

What to automate

Section titled “What to automate”
Test Catches
memlab scenario SPA navigation leaks
Node soak Server module-scope leaks
Listener count assert emitter.listenerCount() after tests

Broken process

Section titled “Broken process”

“We’ll profile manually before each release.”

Fixed process

Section titled “Fixed process”

Leak scenario in CI on every PR touching lifecycle code.