fix(ext/node): implement PerformanceObserver by AndyBodnar · Pull Request #31875 · denoland/deno

AndyBodnar · 2026-01-17T06:39:05Z

Summary

Implements a working PerformanceObserver that properly observes mark and measure entries, addressing the node:perf_hooks compatibility gap.

Adds PerformanceObserver and PerformanceObserverEntryList classes to ext/web/15_performance.js following the W3C Performance Observer spec
Hooks into mark() and measure() to queue entries to observers via microtasks
Updates node polyfill to use the core implementation instead of the previous stubs
Adds comprehensive tests for observe(), disconnect(), takeRecords(), and supportedEntryTypes

Test plan

Added tests in tests/unit_node/perf_hooks_test.ts
Tests cover mark observation, measure observation, disconnect behavior, and takeRecords

Fixes #31723

Implements a working PerformanceObserver that properly observes mark and measure entries, addressing the node:perf_hooks compatibility gap. Changes: - Add PerformanceObserver and PerformanceObserverEntryList classes to ext/web/15_performance.js following the W3C Performance Observer spec - Hook into mark() and measure() to queue entries to observers - Update node polyfill to use the core implementation instead of stubs - Add tests for observe(), disconnect(), takeRecords(), and supportedEntryTypes Fixes denoland#31723

CLAassistant · 2026-01-17T06:39:13Z

All committers have signed the CLA.

- Use ArrayPrototypeIncludes, ArrayPrototypeIndexOf, ArrayPrototypeSplice, ArrayIsArray, and queueMicrotask from primordials - Add supportedEntryTypes static property to PerformanceObserver type definition

AndyBodnar · 2026-01-17T07:29:18Z

Fixed a few issues that came up in CI:

Formatting - Adjusted multi-line formatting for dprint (the filter callbacks and TypeErrors)
Primordials - Switched from global intrinsics to primordials as required by Deno's lint rules:
- Array.isArray() → ArrayIsArray()
- .includes() → ArrayPrototypeIncludes()
- .indexOf() → ArrayPrototypeIndexOf()
- .splice() → ArrayPrototypeSplice()
- Also imported queueMicrotask from primordials
Type definitions - Added the supportedEntryTypes static property to the PerformanceObserver type in cli/tsc/dts/node/perf_hooks.d.cts so TypeScript knows about it

All the release builds passed on first run (macOS, Windows, Linux) - the debug build failures were due to these issues which should be resolved now.

- Change performanceObservers from let to const (array is mutated, not reassigned) - Use ArrayPrototypeSlice instead of .slice()

AndyBodnar · 2026-01-17T07:42:28Z

Two more lint fixes:

Changed let performanceObservers to const (the array is mutated but never reassigned)
Switched .slice() to ArrayPrototypeSlice() for primordials compliance

AndyBodnar · 2026-01-17T08:30:40Z

All CI checks are now passing. Here's a rundown of what was done to get this across the finish line:

The Implementation

Implemented a full PerformanceObserver that follows the W3C spec. The observer hooks into mark() and measure() calls, queues entries to registered observers via microtasks, and properly supports:

observe({ entryTypes: [...] }) - multi-type observation
observe({ type: '...' }) - single-type observation
disconnect() - stops observation and clears the buffer
takeRecords() - synchronously grabs buffered entries
supportedEntryTypes static property - returns ['mark', 'measure']

Fixes Along the Way

dprint formatting - Had to adjust multi-line formatting for filter callbacks and TypeErrors to match the project's style
Primordials - Deno has a lint rule requiring use of primordials to protect against prototype pollution. Switched all array methods to their primordial equivalents:
- Array.isArray() → ArrayIsArray()
- .includes() → ArrayPrototypeIncludes()
- .indexOf() → ArrayPrototypeIndexOf()
- .splice() → ArrayPrototypeSplice()
- .slice() → ArrayPrototypeSlice()
- Also pulled queueMicrotask from primordials
const vs let - Changed let performanceObservers = [] to const since the array reference itself is never reassigned (only mutated)
TypeScript types - Added the supportedEntryTypes static property to the PerformanceObserver class in cli/tsc/dts/node/perf_hooks.d.cts so TypeScript knows it exists

Verification

All 17 CI jobs passed (lint, test, build across Linux/macOS/Windows, x86_64/aarch64, debug/release)
The perf_hooks tests verify mark observation, measure observation, disconnect behavior, takeRecords, and supportedEntryTypes

fraidev · 2026-01-18T14:52:13Z

Hey @AndyBodnar, thanks for the PR! I added a commit to make the node compat tests pass (cargo test --test node_compat -- --filter performanceobserver).

The changes include:

Added NODE_PERFORMANCE_ENTRY_TYPE_* constants to perf_hooks.js, these are used by Node.js internals to track observer counts by entry type (NODE=0, MARK=1, MEASURE=2, GC=3, FUNCTION=4, HTTP2=5, HTTP=6, DNS=7, NET=8)
Added observerCounts to the internal performance binding, the test uses internalBinding('performance').observerCounts to check observer registration counts
Created a Node-compatible PerformanceObserver wrapper, the existing Web API implementation throws generic TypeErrors, but Node.js tests expect errors with code: 'ERR_INVALID_ARG_TYPE'. The wrapper validates:
- Constructor callback must be a function
- observe() options must be an object
- observe() entryTypes must be an array

Now these tests pass:

parallel/test-performance-many-marks.js
parallel/test-performance-measure.js
parallel/test-performanceobserver.js

bartlomieju

Since this PR includes a Web implementation as well, it would be great to add PerformanceObserver and PerformanceObserverEntryList to 98_global_scope_shared.js and enable related WPT tests in tests/wpt/runner/expectation.json - then we'll be able to update https://developer.mozilla.org/en-US/docs/Web/API/PerformanceObserverEntryList and https://developer.mozilla.org/en-US/docs/Web/API/PerformanceObserver to include Deno support. This can be done in a follow up though.

bartlomieju · 2026-01-18T22:05:09Z

tests/unit_node/perf_hooks_test.ts

  assert(typeof performance.markResourceTiming === "function");
 });
+
+Deno.test("[perf_hooks]: PerformanceObserver.supportedEntryTypes", () => {


Looking at the enabled Node compat tests I think these are not necessary and can be removed safely.

tests/node_compat/config.json

AndyBodnar · 2026-01-18T22:21:31Z

Changes made:

Fixed measure() to work without start/end - Removed the check that required start or end in options. Now performance.measure('name', {detail: 'foo'}) works correctly, using startTime=0 and endTime=now() as defaults.
Enabled test-performance-measure-detail.js - Added to Node compat test config.
Removed redundant tests - The basic performance API tests in perf_hooks_test.ts are now covered by the Node compat tests (test-performance-global.js, test-performanceobserver-gc.js).

The global scope additions for WPT tests can be done in a follow-up as suggested.

@bartlomieju

bartlomieju · 2026-01-18T22:25:50Z

@AndyBodnar did you forget to push your changes? None of the described changes are in

- Fix measure() to allow options without start/end (enables test-performance-measure-detail.js) - Enable test-performance-measure-detail.js in Node compat tests - Remove redundant tests covered by Node compat tests

AndyBodnar · 2026-01-18T22:29:13Z

Pushed to the wrong branch earlier - changes are in now.
@bartlomieju

bartlomieju · 2026-01-18T23:39:15Z

Looks like an actual WPT failure, @fraidev can you please take a look?

The Web spec requires start/end for measure options, but Node.js allows measure({detail: ...}) without start/end. Adding this to expected failures since we're implementing Node.js behavior.

AndyBodnar · 2026-01-19T02:08:03Z

Added the WPT test to expected failures. The Web spec requires start/end for measure options, but Node.js allows measure({detail: ...}) without them. Since we're implementing Node.js behavior for test-performance-measure-detail.js, added this to the expectation file.

AndyBodnar · 2026-01-19T03:15:37Z

all checks and tests have passed @bartlomieju

bartlomieju

Thanks!

…List (#31887) Follow up #31875 that exposes Web APIs on the global scope.

AndyBodnar added 2 commits January 17, 2026 00:13

fix: dprint formatting issues

db95ff5

fix: use primordials and add supportedEntryTypes type

a674b82

- Use ArrayPrototypeIncludes, ArrayPrototypeIndexOf, ArrayPrototypeSplice, ArrayIsArray, and queueMicrotask from primordials - Add supportedEntryTypes static property to PerformanceObserver type definition

fix: use const and ArrayPrototypeSlice

6548ff2

- Change performanceObservers from let to const (array is mutated, not reassigned) - Use ArrayPrototypeSlice instead of .slice()

bartlomieju changed the title ~~fix(node/perf_hooks): implement PerformanceObserver~~ fix(ext/node): implement PerformanceObserver Jan 17, 2026

bartlomieju requested a review from fraidev January 17, 2026 09:04

fraidev added 2 commits January 18, 2026 11:46

fix(node/perf_hooks): add missing constants and node error handling

ef29726

chore: format perf_hooks.js

70ae5f7

Merge branch 'main' into fix/perf-observer-node-compat

402a17b

fraidev requested a review from bartlomieju January 18, 2026 17:49

bartlomieju reviewed Jan 18, 2026

View reviewed changes

tests/node_compat/config.json Show resolved Hide resolved

Merge branch 'main' into fix/perf-observer-node-compat

70184e0

Address reviewer feedback for PerformanceObserver

ac9ae02

- Fix measure() to allow options without start/end (enables test-performance-measure-detail.js) - Enable test-performance-measure-detail.js in Node compat tests - Remove redundant tests covered by Node compat tests

birkskyum mentioned this pull request Jan 18, 2026

fix(node): support --conditions in execArgv for child_process.fork #31872

Closed

Add expected WPT failure for measure() with only detail

084669d

The Web spec requires start/end for measure options, but Node.js allows measure({detail: ...}) without start/end. Adding this to expected failures since we're implementing Node.js behavior.

bartlomieju approved these changes Jan 19, 2026

View reviewed changes

bartlomieju merged commit 88341ca into denoland:main Jan 19, 2026
19 checks passed

bartlomieju mentioned this pull request Jan 19, 2026

fix(ext/web): export PerformanceObserver and PerformanceObserverEntryList #31887

Merged

bartlomieju mentioned this pull request Jan 19, 2026

fix(node/perf_hooks): implement PerformanceObserver callbacks #31882

Closed

bartlomieju added a commit that referenced this pull request Jan 20, 2026

fix(ext/web): export PerformanceObserver and PerformanceObserverEntry…

f8df593

…List (#31887) Follow up #31875 that exposes Web APIs on the global scope.

bartlomieju mentioned this pull request Feb 23, 2026

Implement PerformanceObserver.observe from node:perf_hooks #25034

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AndyBodnar commented Jan 17, 2026

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