Node perf_hooks.monitorEventLoopDelay function | API Reference | Bun

This property is an extension by Node.js. It is not available in Web browsers.

Creates an IntervalHistogram object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds.

Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect.

import { monitorEventLoopDelay } from 'node:perf_hooks';
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();
// Do something.
h.disable();
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentiles);
console.log(h.percentile(50));
console.log(h.percentile(99));

The sampling rate in milliseconds. Must be greater than zero.

The number of samples recorded by the histogram.

The number of samples recorded by the histogram. v17.4.0, v16.14.0

The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.

The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.

The maximum recorded event loop delay.

The maximum recorded event loop delay. v17.4.0, v16.14.0

The mean of the recorded event loop delays.

The minimum recorded event loop delay.

The minimum recorded event loop delay. v17.4.0, v16.14.0

Returns a Map object detailing the accumulated percentile distribution.

Returns a Map object detailing the accumulated percentile distribution.

The standard deviation of the recorded event loop delays.

Disables the update interval timer when the histogram is disposed.

const { monitorEventLoopDelay } = require('node:perf_hooks');
{
using hist = monitorEventLoopDelay({ resolution: 20 });
hist.enable();
// The histogram will be disabled when the block is exited.
}

Disables the update interval timer. Returns true if the timer was stopped, false if it was already stopped.

Enables the update interval timer. Returns true if the timer was started, false if it was already started.

Returns the value at the given percentile.

A percentile value in the range (0, 100].

Returns the value at the given percentile.

A percentile value in the range (0, 100].

Resets the collected histogram data.