node:perf_hooks

node:perf_hooks targets Node.js 24.20.0. Jco bundles a TypeScript adaptation of Node’s user timing, resource timing, observer and function timing implementations. It does not use unenv’s placeholder observers or histograms.

Keep ordinary imports in application code:

import { performance, PerformanceObserver } from "node:perf_hooks";

const observer = new PerformanceObserver((entries) => {
  for (const entry of entries.getEntries()) console.log(entry.name, entry.duration);
});
observer.observe({ type: "measure" });
performance.mark("start");
// Application work.
performance.measure("elapsed", "start");

Bundle JavaScript with jco componentize app.js --bundle --wit wit -o app.wasm. The adapter adds no WIT imports. Clock-based operations use the component engine’s monotonic performance.now() and timeOrigin; they fail explicitly if the engine lacks them. Explicit timestamps require no clock. Non-null mark/measure detail requires the engine’s structuredClone implementation. The module owns its timing buffers; it does not replace the engine’s global performance object.

Supported timing operations

Marks, measures (including named marks and start/end/duration options), timeline queries and clearing, explicit resource timings, resource buffer notifications, observers and timerify are implemented. Observers support mark, measure, resource and function entries. Function timing includes promise settlement and constructor calls. Observer and resource-buffer callbacks use component timers; their ordering relative to other tasks can differ from Node’s setImmediate. Resource entries describe timings supplied by the application; network operations are not automatically instrumented.

Native performance telemetry

createHistogram, monitorEventLoopDelay, eventLoopUtilization, performance.nodeTiming and performance.toJSON() throw ERR_JCO_UNSUPPORTED_NODE_API. Components do not expose Node’s HDR histogram binding, libuv event-loop counters or process startup milestones. The histogram option to timerify is consequently unavailable. GC, HTTP, HTTP/2, DNS and network observer instrumentation is unavailable. Deprecated node-entry kind and flags accessors throw ERR_JCO_UNSUPPORTED_DEPRECATED_NODE_API, naming the detail replacement.

The public module exports and constants match the pinned Node 24 surface; APIs introduced in Node 26’s rolling documentation are outside this compatibility target. The source files retain Node’s MIT license and pinned source provenance.

QuickJS currently supplies a clock but lacks task timers and Web event targets. Marks, measures, resource entries within the buffer limit, and synchronous function timing work there. Observer subscription, event listeners and resource buffer overflow fail explicitly; PerformanceObserver.supportedEntryTypes is empty. StarlingMonkey supports these runtime facilities and the observer APIs.