1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
|
# Performance measurement APIs
<!--introduced_in=v8.5.0-->
> Stability: 2 - Stable
<!-- source_link=lib/perf_hooks.js -->
This module provides an implementation of a subset of the W3C
[Web Performance APIs][] as well as additional APIs for
Node.js-specific performance measurements.
Node.js supports the following [Web Performance APIs][]:
* [High Resolution Time][]
* [Performance Timeline][]
* [User Timing][]
```js
const { PerformanceObserver, performance } = require('perf_hooks');
const obs = new PerformanceObserver((items) => {
console.log(items.getEntries()[0].duration);
performance.clearMarks();
});
obs.observe({ type: 'measure' });
performance.measure('Start to Now');
performance.mark('A');
doSomeLongRunningProcess(() => {
performance.measure('A to Now', 'A');
performance.mark('B');
performance.measure('A to B', 'A', 'B');
});
```
## `perf_hooks.performance`
<!-- YAML
added: v8.5.0
-->
An object that can be used to collect performance metrics from the current
Node.js instance. It is similar to [`window.performance`][] in browsers.
### `performance.clearMarks([name])`
<!-- YAML
added: v8.5.0
-->
* `name` {string}
If `name` is not provided, removes all `PerformanceMark` objects from the
Performance Timeline. If `name` is provided, removes only the named mark.
### `performance.eventLoopUtilization([utilization1[, utilization2]])`
<!-- YAML
added:
- v14.10.0
- v12.19.0
-->
* `utilization1` {Object} The result of a previous call to
`eventLoopUtilization()`.
* `utilization2` {Object} The result of a previous call to
`eventLoopUtilization()` prior to `utilization1`.
* Returns {Object}
* `idle` {number}
* `active` {number}
* `utilization` {number}
The `eventLoopUtilization()` method returns an object that contains the
cumulative duration of time the event loop has been both idle and active as a
high resolution milliseconds timer. The `utilization` value is the calculated
Event Loop Utilization (ELU).
If bootstrapping has not yet finished on the main thread the properties have
the value of `0`. The ELU is immediately available on [Worker threads][] since
bootstrap happens within the event loop.
Both `utilization1` and `utilization2` are optional parameters.
If `utilization1` is passed, then the delta between the current call's `active`
and `idle` times, as well as the corresponding `utilization` value are
calculated and returned (similar to [`process.hrtime()`][]).
If `utilization1` and `utilization2` are both passed, then the delta is
calculated between the two arguments. This is a convenience option because,
unlike [`process.hrtime()`][], calculating the ELU is more complex than a
single subtraction.
ELU is similar to CPU utilization, except that it only measures event loop
statistics and not CPU usage. It represents the percentage of time the event
loop has spent outside the event loop's event provider (e.g. `epoll_wait`).
No other CPU idle time is taken into consideration. The following is an example
of how a mostly idle process will have a high ELU.
```js
'use strict';
const { eventLoopUtilization } = require('perf_hooks').performance;
const { spawnSync } = require('child_process');
setImmediate(() => {
const elu = eventLoopUtilization();
spawnSync('sleep', ['5']);
console.log(eventLoopUtilization(elu).utilization);
});
```
Although the CPU is mostly idle while running this script, the value of
`utilization` is `1`. This is because the call to
[`child_process.spawnSync()`][] blocks the event loop from proceeding.
Passing in a user-defined object instead of the result of a previous call to
`eventLoopUtilization()` will lead to undefined behavior. The return values
are not guaranteed to reflect any correct state of the event loop.
### `performance.mark([name[, options]])`
<!-- YAML
added: v8.5.0
changes:
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Updated to conform to the User Timing Level 3 specification.
-->
* `name` {string}
* `options` {Object}
* `detail` {any} Additional optional detail to include with the mark.
* `startTime` {number} An optional timestamp to be used as the mark time.
**Defaults**: `performance.now()`.
Creates a new `PerformanceMark` entry in the Performance Timeline. A
`PerformanceMark` is a subclass of `PerformanceEntry` whose
`performanceEntry.entryType` is always `'mark'`, and whose
`performanceEntry.duration` is always `0`. Performance marks are used
to mark specific significant moments in the Performance Timeline.
### `performance.measure(name[, startMarkOrOptions[, endMark]])`
<!-- YAML
added: v8.5.0
changes:
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Updated to conform to the User Timing Level 3 specification.
- version:
- v13.13.0
- v12.16.3
pr-url: https://github.com/nodejs/node/pull/32651
description: Make `startMark` and `endMark` parameters optional.
-->
* `name` {string}
* `startMarkOrOptions` {string|Object} Optional.
* `detail` {any} Additional optional detail to include with the measure.
* `duration` {number} Duration between start and end times.
* `end` {number|string} Timestamp to be used as the end time, or a string
identifying a previously recorded mark.
* `start` {number|string} Timestamp to be used as the start time, or a string
identifying a previously recorded mark.
* `endMark` {string} Optional. Must be omitted if `startMarkOrOptions` is an
{Object}.
Creates a new `PerformanceMeasure` entry in the Performance Timeline. A
`PerformanceMeasure` is a subclass of `PerformanceEntry` whose
`performanceEntry.entryType` is always `'measure'`, and whose
`performanceEntry.duration` measures the number of milliseconds elapsed since
`startMark` and `endMark`.
The `startMark` argument may identify any *existing* `PerformanceMark` in the
Performance Timeline, or *may* identify any of the timestamp properties
provided by the `PerformanceNodeTiming` class. If the named `startMark` does
not exist, an error is thrown.
The optional `endMark` argument must identify any *existing* `PerformanceMark`
in the Performance Timeline or any of the timestamp properties provided by the
`PerformanceNodeTiming` class. `endMark` will be `performance.now()`
if no parameter is passed, otherwise if the named `endMark` does not exist, an
error will be thrown.
### `performance.nodeTiming`
<!-- YAML
added: v8.5.0
-->
* {PerformanceNodeTiming}
_This property is an extension by Node.js. It is not available in Web browsers._
An instance of the `PerformanceNodeTiming` class that provides performance
metrics for specific Node.js operational milestones.
### `performance.now()`
<!-- YAML
added: v8.5.0
-->
* Returns: {number}
Returns the current high resolution millisecond timestamp, where 0 represents
the start of the current `node` process.
### `performance.timeOrigin`
<!-- YAML
added: v8.5.0
-->
* {number}
The [`timeOrigin`][] specifies the high resolution millisecond timestamp at
which the current `node` process began, measured in Unix time.
### `performance.timerify(fn[, options])`
<!-- YAML
added: v8.5.0
changes:
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37475
description: Added the histogram option.
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Re-implemented to use pure-JavaScript and the ability
to time async functions.
-->
* `fn` {Function}
* `options` {Object}
* `histogram` {RecordableHistogram} A histogram object created using
`perf_hooks.createHistogram()` that will record runtime durations in
nanoseconds.
_This property is an extension by Node.js. It is not available in Web browsers._
Wraps a function within a new function that measures the running time of the
wrapped function. A `PerformanceObserver` must be subscribed to the `'function'`
event type in order for the timing details to be accessed.
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
function someFunction() {
console.log('hello world');
}
const wrapped = performance.timerify(someFunction);
const obs = new PerformanceObserver((list) => {
console.log(list.getEntries()[0].duration);
obs.disconnect();
});
obs.observe({ entryTypes: ['function'] });
// A performance timeline entry will be created
wrapped();
```
If the wrapped function returns a promise, a finally handler will be attached
to the promise and the duration will be reported once the finally handler is
invoked.
### `performance.toJSON()`
<!-- YAML
added: v16.1.0
-->
An object which is JSON representation of the `performance` object. It
is similar to [`window.performance.toJSON`][] in browsers.
## Class: `PerformanceEntry`
<!-- YAML
added: v8.5.0
-->
### `performanceEntry.details`
<!-- YAML
added: v16.0.0
-->
* {any}
Additional detail specific to the `entryType`.
### `performanceEntry.duration`
<!-- YAML
added: v8.5.0
-->
* {number}
The total number of milliseconds elapsed for this entry. This value will not
be meaningful for all Performance Entry types.
### `performanceEntry.entryType`
<!-- YAML
added: v8.5.0
-->
* {string}
The type of the performance entry. It may be one of:
* `'node'` (Node.js only)
* `'mark'` (available on the Web)
* `'measure'` (available on the Web)
* `'gc'` (Node.js only)
* `'function'` (Node.js only)
* `'http2'` (Node.js only)
* `'http'` (Node.js only)
### `performanceEntry.flags`
<!-- YAML
added:
- v13.9.0
- v12.17.0
changes:
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Runtime deprecated. Now moved to the detail property
when entryType is 'gc'.
-->
* {number}
_This property is an extension by Node.js. It is not available in Web browsers._
When `performanceEntry.entryType` is equal to `'gc'`, the `performance.flags`
property contains additional information about garbage collection operation.
The value may be one of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE`
### `performanceEntry.name`
<!-- YAML
added: v8.5.0
-->
* {string}
The name of the performance entry.
### `performanceEntry.kind`
<!-- YAML
added: v8.5.0
changes:
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Runtime deprecated. Now moved to the detail property
when entryType is 'gc'.
-->
* {number}
_This property is an extension by Node.js. It is not available in Web browsers._
When `performanceEntry.entryType` is equal to `'gc'`, the `performance.kind`
property identifies the type of garbage collection operation that occurred.
The value may be one of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB`
### `performanceEntry.startTime`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp marking the starting time of the
Performance Entry.
### Garbage Collection ('gc') Details
When `performanceEntry.type` is equal to `'gc'`, the `performanceEntry.details`
property will be an {Object} with two properties:
* `kind` {number} One of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB`
* `flags` {number} One of:
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY`
* `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE`
### HTTP/2 ('http2') Details
When `performanceEntry.type` is equal to `'http2'`, the
`performanceEntry.details` property will be an {Object} containing
additional performance information.
If `performanceEntry.name` is equal to `Http2Stream`, the `details`
will contain the following properties:
* `bytesRead` {number} The number of `DATA` frame bytes received for this
`Http2Stream`.
* `bytesWritten` {number} The number of `DATA` frame bytes sent for this
`Http2Stream`.
* `id` {number} The identifier of the associated `Http2Stream`
* `timeToFirstByte` {number} The number of milliseconds elapsed between the
`PerformanceEntry` `startTime` and the reception of the first `DATA` frame.
* `timeToFirstByteSent` {number} The number of milliseconds elapsed between
the `PerformanceEntry` `startTime` and sending of the first `DATA` frame.
* `timeToFirstHeader` {number} The number of milliseconds elapsed between the
`PerformanceEntry` `startTime` and the reception of the first header.
If `performanceEntry.name` is equal to `Http2Session`, the `details` will
contain the following properties:
* `bytesRead` {number} The number of bytes received for this `Http2Session`.
* `bytesWritten` {number} The number of bytes sent for this `Http2Session`.
* `framesReceived` {number} The number of HTTP/2 frames received by the
`Http2Session`.
* `framesSent` {number} The number of HTTP/2 frames sent by the `Http2Session`.
* `maxConcurrentStreams` {number} The maximum number of streams concurrently
open during the lifetime of the `Http2Session`.
* `pingRTT` {number} The number of milliseconds elapsed since the transmission
of a `PING` frame and the reception of its acknowledgment. Only present if
a `PING` frame has been sent on the `Http2Session`.
* `streamAverageDuration` {number} The average duration (in milliseconds) for
all `Http2Stream` instances.
* `streamCount` {number} The number of `Http2Stream` instances processed by
the `Http2Session`.
* `type` {string} Either `'server'` or `'client'` to identify the type of
`Http2Session`.
### Timerify ('function') Details
When `performanceEntry.type` is equal to `'function'`, the
`performanceEntry.details` property will be an {Array} listing
the input arguments to the timed function.
## Class: `PerformanceNodeTiming`
<!-- YAML
added: v8.5.0
-->
* Extends: {PerformanceEntry}
_This property is an extension by Node.js. It is not available in Web browsers._
Provides timing details for Node.js itself. The constructor of this class
is not exposed to users.
### `performanceNodeTiming.bootstrapComplete`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the Node.js process
completed bootstrapping. If bootstrapping has not yet finished, the property
has the value of -1.
### `performanceNodeTiming.environment`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the Node.js environment was
initialized.
### `performanceNodeTiming.idleTime`
<!-- YAML
added:
- v14.10.0
- v12.19.0
-->
* {number}
The high resolution millisecond timestamp of the amount of time the event loop
has been idle within the event loop's event provider (e.g. `epoll_wait`). This
does not take CPU usage into consideration. If the event loop has not yet
started (e.g., in the first tick of the main script), the property has the
value of 0.
### `performanceNodeTiming.loopExit`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the Node.js event loop
exited. If the event loop has not yet exited, the property has the value of -1.
It can only have a value of not -1 in a handler of the [`'exit'`][] event.
### `performanceNodeTiming.loopStart`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the Node.js event loop
started. If the event loop has not yet started (e.g., in the first tick of the
main script), the property has the value of -1.
### `performanceNodeTiming.nodeStart`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the Node.js process was
initialized.
### `performanceNodeTiming.v8Start`
<!-- YAML
added: v8.5.0
-->
* {number}
The high resolution millisecond timestamp at which the V8 platform was
initialized.
## Class: `perf_hooks.PerformanceObserver`
### `new PerformanceObserver(callback)`
<!-- YAML
added: v8.5.0
-->
* `callback` {Function}
* `list` {PerformanceObserverEntryList}
* `observer` {PerformanceObserver}
`PerformanceObserver` objects provide notifications when new
`PerformanceEntry` instances have been added to the Performance Timeline.
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const obs = new PerformanceObserver((list, observer) => {
console.log(list.getEntries());
observer.disconnect();
});
obs.observe({ entryTypes: ['mark'], buffered: true });
performance.mark('test');
```
Because `PerformanceObserver` instances introduce their own additional
performance overhead, instances should not be left subscribed to notifications
indefinitely. Users should disconnect observers as soon as they are no
longer needed.
The `callback` is invoked when a `PerformanceObserver` is
notified about new `PerformanceEntry` instances. The callback receives a
`PerformanceObserverEntryList` instance and a reference to the
`PerformanceObserver`.
### `performanceObserver.disconnect()`
<!-- YAML
added: v8.5.0
-->
Disconnects the `PerformanceObserver` instance from all notifications.
### `performanceObserver.observe(options)`
<!-- YAML
added: v8.5.0
changes:
- version: v16.7.0
pr-url: https://github.com/nodejs/node/pull/39297
description: Updated to conform to Performance Timeline Level 2. The
buffered option has been added back.
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/37136
description: Updated to conform to User Timing Level 3. The
buffered option has been removed.
-->
* `options` {Object}
* `type` {string} A single {PerformanceEntry} type. Must not be given
if `entryTypes` is already specified.
* `entryTypes` {string[]} An array of strings identifying the types of
{PerformanceEntry} instances the observer is interested in. If not
provided an error will be thrown.
* `buffered` {boolean} If true, the observer callback is called with a
list global `PerformanceEntry` buffered entries. If false, only
`PerformanceEntry`s created after the time point are sent to the
observer callback. **Default:** `false`.
Subscribes the {PerformanceObserver} instance to notifications of new
{PerformanceEntry} instances identified either by `options.entryTypes`
or `options.type`:
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const obs = new PerformanceObserver((list, observer) => {
// Called three times synchronously. `list` contains one item.
});
obs.observe({ type: 'mark' });
for (let n = 0; n < 3; n++)
performance.mark(`test${n}`);
```
## Class: `PerformanceObserverEntryList`
<!-- YAML
added: v8.5.0
-->
The `PerformanceObserverEntryList` class is used to provide access to the
`PerformanceEntry` instances passed to a `PerformanceObserver`.
The constructor of this class is not exposed to users.
### `performanceObserverEntryList.getEntries()`
<!-- YAML
added: v8.5.0
-->
* Returns: {PerformanceEntry[]}
Returns a list of `PerformanceEntry` objects in chronological order
with respect to `performanceEntry.startTime`.
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntries());
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 81.465639,
* duration: 0
* },
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 81.860064,
* duration: 0
* }
* ]
*/
observer.disconnect();
});
obs.observe({ type: 'mark' });
performance.mark('test');
performance.mark('meow');
```
### `performanceObserverEntryList.getEntriesByName(name[, type])`
<!-- YAML
added: v8.5.0
-->
* `name` {string}
* `type` {string}
* Returns: {PerformanceEntry[]}
Returns a list of `PerformanceEntry` objects in chronological order
with respect to `performanceEntry.startTime` whose `performanceEntry.name` is
equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to
`type`.
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntriesByName('meow'));
/**
* [
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 98.545991,
* duration: 0
* }
* ]
*/
console.log(perfObserverList.getEntriesByName('nope')); // []
console.log(perfObserverList.getEntriesByName('test', 'mark'));
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 63.518931,
* duration: 0
* }
* ]
*/
console.log(perfObserverList.getEntriesByName('test', 'measure')); // []
observer.disconnect();
});
obs.observe({ entryTypes: ['mark', 'measure'] });
performance.mark('test');
performance.mark('meow');
```
### `performanceObserverEntryList.getEntriesByType(type)`
<!-- YAML
added: v8.5.0
-->
* `type` {string}
* Returns: {PerformanceEntry[]}
Returns a list of `PerformanceEntry` objects in chronological order
with respect to `performanceEntry.startTime` whose `performanceEntry.entryType`
is equal to `type`.
```js
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const obs = new PerformanceObserver((perfObserverList, observer) => {
console.log(perfObserverList.getEntriesByType('mark'));
/**
* [
* PerformanceEntry {
* name: 'test',
* entryType: 'mark',
* startTime: 55.897834,
* duration: 0
* },
* PerformanceEntry {
* name: 'meow',
* entryType: 'mark',
* startTime: 56.350146,
* duration: 0
* }
* ]
*/
observer.disconnect();
});
obs.observe({ type: 'mark' });
performance.mark('test');
performance.mark('meow');
```
## `perf_hooks.createHistogram([options])`
<!-- YAML
added: v15.9.0
-->
* `options` {Object}
* `min` {number|bigint} The minimum recordable value. Must be an integer
value greater than 0. **Default:** `1`.
* `max` {number|bigint} The maximum recordable value. Must be an integer
value greater than `min`. **Default:** `Number.MAX_SAFE_INTEGER`.
* `figures` {number} The number of accuracy digits. Must be a number between
`1` and `5`. **Default:** `3`.
* Returns {RecordableHistogram}
Returns a {RecordableHistogram}.
## `perf_hooks.monitorEventLoopDelay([options])`
<!-- YAML
added: v11.10.0
-->
* `options` {Object}
* `resolution` {number} The sampling rate in milliseconds. Must be greater
than zero. **Default:** `10`.
* Returns: {IntervalHistogram}
_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.
```js
const { monitorEventLoopDelay } = require('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));
```
## Class: `Histogram`
<!-- YAML
added: v11.10.0
-->
### `histogram.exceeds`
<!-- YAML
added: v11.10.0
-->
* {number}
The number of times the event loop delay exceeded the maximum 1 hour event
loop delay threshold.
### `histogram.max`
<!-- YAML
added: v11.10.0
-->
* {number}
The maximum recorded event loop delay.
### `histogram.mean`
<!-- YAML
added: v11.10.0
-->
* {number}
The mean of the recorded event loop delays.
### `histogram.min`
<!-- YAML
added: v11.10.0
-->
* {number}
The minimum recorded event loop delay.
### `histogram.percentile(percentile)`
<!-- YAML
added: v11.10.0
-->
* `percentile` {number} A percentile value in the range (0, 100].
* Returns: {number}
Returns the value at the given percentile.
### `histogram.percentiles`
<!-- YAML
added: v11.10.0
-->
* {Map}
Returns a `Map` object detailing the accumulated percentile distribution.
### `histogram.reset()`
<!-- YAML
added: v11.10.0
-->
Resets the collected histogram data.
### `histogram.stddev`
<!-- YAML
added: v11.10.0
-->
* {number}
The standard deviation of the recorded event loop delays.
## Class: `IntervalHistogram extends Histogram`
A `Histogram` that is periodically updated on a given interval.
### `histogram.disable()`
<!-- YAML
added: v11.10.0
-->
* Returns: {boolean}
Disables the update interval timer. Returns `true` if the timer was
stopped, `false` if it was already stopped.
### `histogram.enable()`
<!-- YAML
added: v11.10.0
-->
* Returns: {boolean}
Enables the update interval timer. Returns `true` if the timer was
started, `false` if it was already started.
### Cloning an `IntervalHistogram`
{IntervalHistogram} instances can be cloned via {MessagePort}. On the receiving
end, the histogram is cloned as a plain {Histogram} object that does not
implement the `enable()` and `disable()` methods.
## Class: `RecordableHistogram extends Histogram`
<!-- YAML
added: v15.9.0
-->
### `histogram.record(val)`
<!-- YAML
added: v15.9.0
-->
* `val` {number|bigint} The amount to record in the histogram.
### `histogram.recordDelta()`
<!-- YAML
added: v15.9.0
-->
Calculates the amount of time (in nanoseconds) that has passed since the
previous call to `recordDelta()` and records that amount in the histogram.
## Examples
### Measuring the duration of async operations
The following example uses the [Async Hooks][] and Performance APIs to measure
the actual duration of a Timeout operation (including the amount of time it took
to execute the callback).
```js
'use strict';
const async_hooks = require('async_hooks');
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const set = new Set();
const hook = async_hooks.createHook({
init(id, type) {
if (type === 'Timeout') {
performance.mark(`Timeout-${id}-Init`);
set.add(id);
}
},
destroy(id) {
if (set.has(id)) {
set.delete(id);
performance.mark(`Timeout-${id}-Destroy`);
performance.measure(`Timeout-${id}`,
`Timeout-${id}-Init`,
`Timeout-${id}-Destroy`);
}
}
});
hook.enable();
const obs = new PerformanceObserver((list, observer) => {
console.log(list.getEntries()[0]);
performance.clearMarks();
observer.disconnect();
});
obs.observe({ entryTypes: ['measure'], buffered: true });
setTimeout(() => {}, 1000);
```
### Measuring how long it takes to load dependencies
The following example measures the duration of `require()` operations to load
dependencies:
<!-- eslint-disable no-global-assign -->
```js
'use strict';
const {
performance,
PerformanceObserver
} = require('perf_hooks');
const mod = require('module');
// Monkey patch the require function
mod.Module.prototype.require =
performance.timerify(mod.Module.prototype.require);
require = performance.timerify(require);
// Activate the observer
const obs = new PerformanceObserver((list) => {
const entries = list.getEntries();
entries.forEach((entry) => {
console.log(`require('${entry[0]}')`, entry.duration);
});
obs.disconnect();
});
obs.observe({ entryTypes: ['function'], buffered: true });
require('some-module');
```
[Async Hooks]: async_hooks.md
[High Resolution Time]: https://www.w3.org/TR/hr-time-2
[Performance Timeline]: https://w3c.github.io/performance-timeline/
[User Timing]: https://www.w3.org/TR/user-timing/
[Web Performance APIs]: https://w3c.github.io/perf-timing-primer/
[Worker threads]: worker_threads.md#worker-threads
[`'exit'`]: process.md#event-exit
[`child_process.spawnSync()`]: child_process.md#child_processspawnsynccommand-args-options
[`process.hrtime()`]: process.md#processhrtimetime
[`timeOrigin`]: https://w3c.github.io/hr-time/#dom-performance-timeorigin
[`window.performance.toJSON`]: https://developer.mozilla.org/en-US/docs/Web/API/Performance/toJSON
[`window.performance`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/performance
|