Javascript Performance

JavaScript Performance

Use When

• Profiling Node.js or browser JavaScript for CPU, memory, or responsiveness issues.
• Investigating event loop stalls, GC pauses, or memory leaks.
• Optimizing async control flow and concurrency.

Profiling Tools

1. Node.js profiling

• CPU: node --prof then node --prof-process --preprocess for flame graphs.
• Memory: Start with node --inspect and Chrome DevTools heap snapshots.
• Real-time: Use clinic.js or 0x for interactive profiles.

1. Event loop and async analysis

• Trace event loop: Use --trace-events flag and analyze in Chrome DevTools.
• Async hooks: Use async_hooks module to detect blocking or slow async operations.
• Benchmark libraries: benchmark.js for micro-benchmarks, custom timers for macro.

1. Memory profiling

• Heap snapshots: Chrome DevTools or heapdump package.
• Allocation timeline: See where memory is allocated over time.
• GC statistics: Use --trace-gc to see pause times and frequency.

Checklist

1. Event loop efficiency

• Are any operations blocking the event loop (synchronous I/O, tight loops)?
• Is work properly chunked with setImmediate when needed?
• Are there unnecessary await points or promise chains?

1. Concurrency and throughput

• Is concurrency limited by connection/resource pools?
• Are operations properly parallelized (Promise.all) or sequenced incorrectly?
• Check for lock contention in shared state or database pools.

1. Memory management

• Are objects retained longer than needed (circular references, forgotten listeners)?
• Is memory growing unbounded or within expected bounds?
• Are timers, listeners, or streams properly cleaned up?

1. Garbage collection

• Is GC pause time acceptable for your workload?
• Are large objects or frequent allocations causing GC pressure?
• Consider using --max-old-space-size if running large workloads.

Output Requirements

For each finding provide:

• Measurement (baseline throughput, latency, memory).
• Profiling evidence (flame graph, trace, heap snapshot).
• Root cause and impact.
• Optimization strategy and expected improvement.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: caraya
• Source: caraya/agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.