## Summary
This PR implements `perf_hooks.monitorEventLoopDelay()` for Node.js
compatibility, enabling monitoring of event loop delays and collection
of performance metrics via histograms.
Fixes#17650
## Implementation Details
### JavaScript Layer (`perf_hooks.ts`)
- Added `IntervalHistogram` class with:
- `enable()` / `disable()` methods with proper state tracking
- `reset()` method to clear histogram data
- Properties: `min`, `max`, `mean`, `stddev`, `exceeds`, `percentiles`
- `percentile(p)` method with validation
- Full input validation matching Node.js behavior (TypeError vs
RangeError)
### C++ Bindings (`JSNodePerformanceHooksHistogramPrototype.cpp`)
- `jsFunction_monitorEventLoopDelay` - Creates histogram for event loop
monitoring
- `jsFunction_enableEventLoopDelay` - Enables monitoring and starts
timer
- `jsFunction_disableEventLoopDelay` - Disables monitoring and stops
timer
- `JSNodePerformanceHooksHistogram_recordDelay` - Records delay
measurements
### Zig Implementation (`EventLoopDelayMonitor.zig`)
- Embedded `EventLoopTimer` that fires periodically based on resolution
- Tracks last fire time and calculates delay between expected vs actual
- Records delays > 0 to the histogram
- Integrates seamlessly with existing Timer system
## Testing
✅ All tests pass:
- Custom test suite with 8 comprehensive tests
- Adapted Node.js core test for full compatibility
- Tests cover enable/disable behavior, percentiles, error handling, and
delay recording
## Test plan
- [x] Run `bun test
test/js/node/perf_hooks/test-monitorEventLoopDelay.test.js`
- [x] Run adapted Node.js test
`test/js/node/test/sequential/test-performance-eventloopdelay-adapted.test.js`
- [x] Verify proper error handling for invalid arguments
- [x] Confirm delay measurements are recorded correctly
🤖 Generated with [Claude Code](https://claude.ai/code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
