[Web Site Performance] Continuous CPU usage and memory leak on neetcode.io (Monaco Editor + PostHog/NgZone)

[Ali-Al-Hadi-Al-Husseini]

Description

The neetcode.io website exhibits significant performance degradation when left idle. Specifically, the site causes continuous high CPU usage and a steady memory leak, even when no user interaction is occurring.

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Environment

• Browser: Safari 26.4
• OS: macOS Tahoe 26.4.1

Symptoms

• High Energy Impact: Safari reports "High" energy usage immediately.
• Memory Leak: The Safari Web Content process climbs to ~1.1 GB RAM within minutes on an idle page.
• CPU Spikes: Sustained CPU usage between 37–142% while idle.

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memory usage I monitored on activity monitor

Investigation & Technical Analysis

I collected profiler data and intercepted console traces . To assist in parsing the dense stack traces and identifying patterns within the RxJS observables, I used Claude to analyze the performance snapshots. This collaboration pinpointed two distinct causes:Analysis of the performance snapshots pinpointed two distinct causes:

1. Monaco Editor ResizeObserver Loop (Primary Cause)

The Monaco editor instance (8101.ceb05aeae98ec630.js) has a ResizeObserver on its container that fires in a tight loop. This schedules a requestAnimationFrame on every frame (~60/sec) even when the page is idle.

• Trace: measureReferenceDomElement → _recomputeOptions → fire → endEmitViewEvents → _scheduleRender → requestAnimationFrame.
• Error: Safari Console reports: ResizeObserver loop completed with undelivered notifications. (x19)

2. PostHog inside Angular's NgZone (Compounding Cause)

posthog-recorder.js registers a setInterval inside Angular's NgZone. Because it runs inside the zone, every flush cycle triggers Angular Change Detection. This prevents the application from reaching a "stable" state, compounding the composite/paint loop caused by the Monaco editor.

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Suggested Fixes

1. Debounce Monaco ResizeObserver

Break the infinite loop by debouncing the layout call or triggering it only on actual window resize events.

const resizeObserver = new ResizeObserver(
  debounce(() => editor.layout(), 100)
);

2. Run PostHog Outside Angular Zone

Initialize the PostHog SDK outside of NgZone so that its internal timers and polling do not trigger unnecessary Change Detection cycles.

constructor(private ngZone: NgZone) {
  this.ngZone.runOutsideAngular(() => {
    posthog.init('YOUR_KEY', { ... });
  });
}

Supporting Evidence

Timeline Data: 1,763 GPU composite events recorded in 30 seconds (~117/sec) on an idle page.

Layout Thrashing: 21 forced layouts detected during the recording period.
unable to upload json file because of the large size > 150mb

[Ali-Al-Hadi-Al-Husseini]

for me it crashes around 4gb usage I have 18 gb ram