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JS Memory Leak School

performance.memory

Chromium exposes non-standard performance.memory:

{
  jsHeapSizeLimit: 4294705152,
  totalJSHeapSize: 35839476,
  usedJSHeapSize: 25031212
}

Our browser demos poll usedJSHeapSize every second for the live chart.

Usage

Section titled “Usage”
function heapMb() {
  if (!performance.memory) return null;
  return (performance.memory.usedJSHeapSize / 1024 / 1024).toFixed(1);
}


setInterval(() => console.log(`${heapMb()} MB`), 1000);

Limitations

Section titled “Limitations”
Limitation Detail
Chromium only Not in Firefox/Safari
Approximate Rounded for security
Not for production RUM Use PerformanceObserver + your backend carefully

Enable in headless Chrome

Section titled “Enable in headless Chrome”
Terminal window
chrome --enable-precise-memory-info

Broken interpretation

Section titled “Broken interpretation”

“Topped 100 MB once → leak!” — could be one-time load.

Healthy interpretation

Section titled “Healthy interpretation”

Track slope over repeated identical actions after GC.