JS Heap Size Limit

Maximum JS Heap Size

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Note: Chrome-only. Maximum memory the JavaScript engine can allocate.

1. Technical Classification

Performance APIChrome-onlyMemory LimitSystem Info

The jsHeapSizeLimit property reveals the maximum amount of memory the JavaScript engine will allocate before triggering out-of-memory errors. This limit is based on system RAM and browser architecture (32-bit vs 64-bit).

System-dependent: Varies by available RAM and browser type
Static value: Doesn't change during page lifetime
Chrome-only: Not in standard spec, Firefox/Safari don't expose this
Architecture-dependent: 32-bit vs 64-bit browsers have different limits

2. Background & Purpose

This was added alongside usedJSHeapSize to help developers understand memory constraints. Knowing the limit helps developers design applications that won't crash due to memory exhaustion.

Why It Exists

Memory planning: Design apps within memory constraints
Error handling: Detect approaching limits and take action
Optimization: Know when to free up memory

3. Possible Values & Detection

Typical Limits

32-bit Chrome

~512 MB - Limited by 32-bit address space

64-bit Chrome (4GB RAM)

~1-2 GB - Limited by available system memory

64-bit Chrome (16GB+ RAM)

~4 GB - Generous limit on high-memory systems

Detection Code

if (performance.memory) {
  const limitMB = Math.round(performance.memory.jsHeapSizeLimit / 1024 / 1024);
  console.log('Heap limit:', limitMB, 'MB');
}

4. Common Legitimate Uses

Application Development

Memory budgeting: Design within known constraints
Feature gating: Disable memory-intensive features on low-memory devices
Warning systems: Alert users before memory exhaustion

5. Browser & Platform Differences

System	Typical Limit	Notes
64-bit Chrome (16GB RAM)	4096 MB	High-memory desktop
64-bit Chrome (8GB RAM)	2048 MB	Standard laptop
64-bit Chrome (4GB RAM)	1024-1536 MB	Low-memory device
32-bit Chrome	512 MB	Architectural limit
Mobile Chrome	256-512 MB	Limited by mobile RAM
Firefox/Safari	N/A	API not available

6. Privacy Implications & Tracking Risks

Privacy Risk: LOW-MEDIUM

Heap limit reveals system memory tier, helping fingerprint device type and specifications.

What It Reveals

System RAM: Approximate installed memory
Architecture: 32-bit vs 64-bit browser
Device tier: Budget vs high-end system

While not uniquely identifying, this contributes to device fingerprinting by narrowing down system specifications.

7. How to Control This Feature

Limited control options:

Use Firefox/Safari: Don't expose this API
Not configurable in Chrome: No browser setting to disable
Use privacy browsers: Brave may normalize this value

8. Learn More

MDN: performance.memoryDocumentation for the memory API V8: Heap Size LimitsTechnical details on V8 memory limits