Add __spreadArrays helper by rbuckton · Pull Request #31166 · microsoft/TypeScript · GitHub

Adds a __spreadArrays helper for a more accurate spread behavior when not using --downlevelIteration.

TypeScript Bot (@typescript-bot) perf test

Heya Ron Buckton (@rbuckton), I've started to run the perf test suite on this PR at 528601f. You can monitor the build here. It should now contribute to this PR's status checks.

Update: The results are in!

Ron Buckton (@rbuckton)
The results of the perf run you requested are in!

Here they are:

Comparison Report - master..31166

Metric	master	31166	Delta	Best	Worst
Angular - node (v12.1.0, x64)
Memory used	313,388k (± 0.02%)	313,430k (± 0.02%)	+42k (+ 0.01%)	313,303k	313,531k
Parse Time	1.38s (± 0.68%)	1.42s (± 0.94%)	+0.04s (+ 2.83%)	1.40s	1.45s
Bind Time	0.73s (± 0.65%)	0.74s (± 1.13%)	+0.00s (+ 0.27%)	0.72s	0.75s
Check Time	3.96s (± 0.59%)	3.98s (± 0.40%)	+0.02s (+ 0.40%)	3.94s	4.00s
Emit Time	5.14s (± 0.82%)	5.14s (± 0.51%)	+0.00s (+ 0.06%)	5.08s	5.19s
Total Time	11.21s (± 0.54%)	11.27s (± 0.40%)	+0.06s (+ 0.51%)	11.15s	11.34s
Monaco - node (v12.1.0, x64)
Memory used	341,959k (± 0.02%)	342,000k (± 0.02%)	+41k (+ 0.01%)	341,868k	342,106k
Parse Time	1.17s (± 0.66%)	1.19s (± 0.52%)	+0.02s (+ 1.71%)	1.18s	1.20s
Bind Time	0.67s (± 0.97%)	0.67s (± 1.41%)	+0.01s (+ 0.90%)	0.66s	0.70s
Check Time	4.06s (± 0.51%)	4.04s (± 0.43%)	-0.02s (- 0.42%)	4.00s	4.09s
Emit Time	2.77s (± 0.59%)	2.76s (± 0.58%)	-0.00s (- 0.14%)	2.74s	2.80s
Total Time	8.66s (± 0.30%)	8.67s (± 0.32%)	+0.01s (+ 0.12%)	8.62s	8.74s
TFS - node (v12.1.0, x64)
Memory used	298,947k (± 0.01%)	298,897k (± 0.03%)	-51k (- 0.02%)	298,743k	299,064k
Parse Time	0.92s (± 0.74%)	0.92s (± 0.96%)	+0.01s (+ 0.87%)	0.90s	0.95s
Bind Time	0.62s (± 0.93%)	0.62s (± 0.60%)	-0.00s (- 0.81%)	0.61s	0.62s
Check Time	3.62s (± 0.41%)	3.64s (± 0.55%)	+0.02s (+ 0.58%)	3.58s	3.67s
Emit Time	2.86s (± 0.85%)	2.85s (± 0.86%)	-0.00s (- 0.14%)	2.78s	2.91s
Total Time	8.01s (± 0.41%)	8.03s (± 0.43%)	+0.02s (+ 0.27%)	7.94s	8.10s
Angular - node (v8.9.0, x64)
Memory used	330,848k (± 0.02%)	330,894k (± 0.02%)	+46k (+ 0.01%)	330,786k	331,042k
Parse Time	1.78s (± 0.47%)	1.79s (± 0.27%)	+0.02s (+ 1.01%)	1.78s	1.80s
Bind Time	0.79s (± 0.98%)	0.80s (± 0.86%)	+0.01s (+ 0.63%)	0.78s	0.81s
Check Time	4.66s (± 1.58%)	4.62s (± 1.42%)	-0.04s (- 0.90%)	4.48s	4.75s
Emit Time	5.88s (± 2.75%)	5.88s (± 2.64%)	+0.00s (+ 0.03%)	5.60s	6.18s
Total Time	13.11s (± 0.98%)	13.09s (± 0.98%)	-0.02s (- 0.16%)	12.85s	13.33s
Monaco - node (v8.9.0, x64)
Memory used	358,630k (± 0.02%)	358,689k (± 0.02%)	+59k (+ 0.02%)	358,503k	358,904k
Parse Time	1.43s (± 0.34%)	1.45s (± 0.54%)	+0.01s (+ 1.05%)	1.42s	1.46s
Bind Time	0.92s (± 0.67%)	0.90s (± 1.40%)	-0.03s (- 2.82%)	0.87s	0.91s
Check Time	4.73s (± 0.45%)	4.86s (± 1.76%)	+0.13s (+ 2.72%)	4.73s	5.04s
Emit Time	3.40s (± 0.54%)	3.15s (± 6.58%)	-0.25s (- 7.38%)	2.80s	3.40s
Total Time	10.49s (± 0.32%)	10.36s (± 1.36%)	-0.13s (- 1.23%)	10.10s	10.56s
TFS - node (v8.9.0, x64)
Memory used	314,046k (± 0.01%)	314,055k (± 0.01%)	+9k (+ 0.00%)	313,962k	314,165k
Parse Time	1.14s (± 0.54%)	1.14s (± 0.77%)	+0.00s (+ 0.35%)	1.13s	1.17s
Bind Time	0.66s (± 0.61%)	0.67s (± 1.12%)	+0.01s (+ 0.91%)	0.65s	0.69s
Check Time	4.19s (± 0.40%)	4.22s (± 0.63%)	+0.03s (+ 0.62%)	4.17s	4.26s
Emit Time	3.13s (± 0.61%)	3.12s (± 0.51%)	-0.00s (- 0.13%)	3.09s	3.17s
Total Time	9.12s (± 0.35%)	9.15s (± 0.37%)	+0.03s (+ 0.35%)	9.08s	9.21s
Angular - node (v8.9.0, x86)
Memory used	187,343k (± 0.02%)	187,360k (± 0.02%)	+17k (+ 0.01%)	187,282k	187,438k
Parse Time	1.72s (± 0.80%)	1.75s (± 0.58%)	+0.04s (+ 2.04%)	1.73s	1.77s
Bind Time	0.93s (± 0.74%)	0.93s (± 1.97%)	-0.00s (- 0.11%)	0.89s	0.98s
Check Time	4.30s (± 0.50%)	4.30s (± 0.31%)	-0.01s (- 0.19%)	4.27s	4.33s
Emit Time	5.64s (± 1.17%)	5.64s (± 1.19%)	+0.00s (+ 0.02%)	5.51s	5.77s
Total Time	12.59s (± 0.73%)	12.61s (± 0.62%)	+0.03s (+ 0.21%)	12.44s	12.78s
Monaco - node (v8.9.0, x86)
Memory used	200,012k (± 0.01%)	200,027k (± 0.02%)	+14k (+ 0.01%)	199,920k	200,088k
Parse Time	1.48s (± 0.55%)	1.51s (± 0.84%)	+0.03s (+ 1.96%)	1.48s	1.54s
Bind Time	0.72s (± 2.43%)	0.71s (± 0.73%)	-0.01s (- 1.80%)	0.70s	0.72s
Check Time	4.62s (± 0.60%)	4.62s (± 0.51%)	+0.00s (+ 0.02%)	4.55s	4.65s
Emit Time	3.09s (± 0.57%)	3.07s (± 0.45%)	-0.01s (- 0.39%)	3.05s	3.12s
Total Time	9.90s (± 0.37%)	9.91s (± 0.29%)	+0.01s (+ 0.09%)	9.85s	9.97s
TFS - node (v8.9.0, x86)
Memory used	176,085k (± 0.03%)	176,092k (± 0.02%)	+8k (+ 0.00%)	176,007k	176,198k
Parse Time	1.18s (± 1.01%)	1.21s (± 1.00%)	+0.02s (+ 2.03%)	1.19s	1.24s
Bind Time	0.63s (± 0.94%)	0.63s (± 0.75%)	-0.00s (- 0.63%)	0.62s	0.64s
Check Time	4.04s (± 0.52%)	4.06s (± 0.89%)	+0.02s (+ 0.45%)	3.99s	4.12s
Emit Time	2.75s (± 1.24%)	2.73s (± 1.22%)	-0.02s (- 0.76%)	2.68s	2.83s
Total Time	8.61s (± 0.64%)	8.63s (± 0.76%)	+0.02s (+ 0.20%)	8.48s	8.73s
Angular - node (v9.0.0, x64)
Memory used	330,616k (± 0.02%)	330,548k (± 0.02%)	-69k (- 0.02%)	330,446k	330,693k
Parse Time	1.62s (± 0.50%)	1.63s (± 0.29%)	+0.01s (+ 0.43%)	1.62s	1.64s
Bind Time	0.74s (± 1.11%)	0.74s (± 0.90%)	-0.01s (- 0.67%)	0.73s	0.75s
Check Time	4.34s (± 0.48%)	4.31s (± 0.53%)	-0.03s (- 0.67%)	4.25s	4.38s
Emit Time	5.73s (± 1.77%)	5.71s (± 1.77%)	-0.02s (- 0.40%)	5.51s	5.91s
Total Time	12.44s (± 1.01%)	12.39s (± 0.82%)	-0.05s (- 0.36%)	12.19s	12.60s
Monaco - node (v9.0.0, x64)
Memory used	358,518k (± 0.02%)	358,607k (± 0.02%)	+89k (+ 0.02%)	358,411k	358,736k
Parse Time	1.28s (± 0.71%)	1.29s (± 0.53%)	+0.01s (+ 1.01%)	1.28s	1.31s
Bind Time	0.85s (± 0.40%)	0.85s (± 0.70%)	-0.01s (- 0.82%)	0.84s	0.86s
Check Time	4.68s (± 0.47%)	4.71s (± 0.37%)	+0.02s (+ 0.49%)	4.68s	4.75s
Emit Time	3.27s (± 1.63%)	3.28s (± 0.51%)	+0.01s (+ 0.40%)	3.23s	3.30s
Total Time	10.09s (± 0.73%)	10.13s (± 0.30%)	+0.04s (+ 0.39%)	10.03s	10.18s
TFS - node (v9.0.0, x64)
Memory used	313,931k (± 0.02%)	313,909k (± 0.02%)	-22k (- 0.01%)	313,799k	314,070k
Parse Time	1.00s (± 0.33%)	1.01s (± 0.37%)	+0.01s (+ 1.50%)	1.01s	1.02s
Bind Time	0.62s (± 0.77%)	0.61s (± 0.95%)	-0.00s (- 0.65%)	0.60s	0.63s
Check Time	4.23s (± 2.06%)	4.24s (± 2.17%)	+0.01s (+ 0.19%)	4.12s	4.45s
Emit Time	2.97s (± 3.30%)	2.98s (± 3.20%)	+0.02s (+ 0.54%)	2.82s	3.14s
Total Time	8.81s (± 0.47%)	8.85s (± 0.39%)	+0.04s (+ 0.44%)	8.76s	8.91s
Angular - node (v9.0.0, x86)
Memory used	187,522k (± 0.03%)	187,512k (± 0.03%)	-10k (- 0.01%)	187,396k	187,658k
Parse Time	1.54s (± 0.58%)	1.57s (± 0.86%)	+0.04s (+ 2.35%)	1.55s	1.61s
Bind Time	0.86s (± 0.55%)	0.89s (± 0.77%)	+0.03s (+ 2.91%)	0.87s	0.90s
Check Time	4.01s (± 0.54%)	4.05s (± 0.65%)	+0.04s (+ 0.95%)	4.00s	4.13s
Emit Time	5.33s (± 0.79%)	5.39s (± 0.76%)	+0.06s (+ 1.20%)	5.32s	5.53s
Total Time	11.73s (± 0.40%)	11.89s (± 0.65%)	+0.16s (+ 1.36%)	11.79s	12.16s
Monaco - node (v9.0.0, x86)
Memory used	200,072k (± 0.03%)	200,057k (± 0.02%)	-14k (- 0.01%)	199,996k	200,211k
Parse Time	1.31s (± 0.58%)	1.33s (± 0.60%)	+0.02s (+ 1.76%)	1.31s	1.35s
Bind Time	0.64s (± 0.90%)	0.64s (± 1.41%)	+0.00s (+ 0.16%)	0.63s	0.67s
Check Time	4.48s (± 0.29%)	4.48s (± 0.40%)	-0.00s (- 0.04%)	4.43s	4.50s
Emit Time	2.99s (± 0.37%)	3.00s (± 0.69%)	+0.01s (+ 0.20%)	2.96s	3.06s
Total Time	9.41s (± 0.20%)	9.44s (± 0.31%)	+0.02s (+ 0.27%)	9.39s	9.52s
TFS - node (v9.0.0, x86)
Memory used	176,172k (± 0.02%)	176,236k (± 0.02%)	+64k (+ 0.04%)	176,139k	176,319k
Parse Time	1.03s (± 1.53%)	1.04s (± 0.66%)	+0.01s (+ 0.68%)	1.02s	1.05s
Bind Time	0.57s (± 1.43%)	0.58s (± 0.77%)	+0.01s (+ 0.87%)	0.57s	0.59s
Check Time	3.89s (± 0.69%)	3.92s (± 0.63%)	+0.03s (+ 0.77%)	3.88s	4.00s
Emit Time	2.69s (± 0.71%)	2.71s (± 0.89%)	+0.02s (+ 0.63%)	2.66s	2.76s
Total Time	8.18s (± 0.62%)	8.24s (± 0.38%)	+0.06s (+ 0.76%)	8.17s	8.30s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-142-generic
Architecture	x64
Available Memory	16 GB
Available Memory	1 GB
CPUs	4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz

Hosts

node (v12.1.0, x64)
node (v8.9.0, x64)
node (v8.9.0, x86)
node (v9.0.0, x64)
node (v9.0.0, x86)

Scenarios

Angular - node (v12.1.0, x64)
Angular - node (v8.9.0, x64)
Angular - node (v8.9.0, x86)
Angular - node (v9.0.0, x64)
Angular - node (v9.0.0, x86)
Monaco - node (v12.1.0, x64)
Monaco - node (v8.9.0, x64)
Monaco - node (v8.9.0, x86)
Monaco - node (v9.0.0, x64)
Monaco - node (v9.0.0, x86)
TFS - node (v12.1.0, x64)
TFS - node (v8.9.0, x64)
TFS - node (v8.9.0, x86)
TFS - node (v9.0.0, x64)
TFS - node (v9.0.0, x86)

Benchmark	Name	Iterations
Current	31166	10
Baseline	master	10

What about speedup __spreadArrays?

var __spreadArrays = function () {
  for (var i = 0, l = 0, al = arguments.length; i < al; ++i)
    l += arguments[i].length;
  for (var ar = new Array(l), i = 0, k = 0; i < al; ++i)
    for (var j = 0, a = arguments[i], jl = a.length; j < jl; ++j, ++k)
      ar[k] = a[j];
  return ar;
};

On V8 7.4 this faster by ~3x-6x for large (> 1k) arrays.

Bench link:
https://esbench.com/bench/5cc9a0f14cd7e6009ef62323

const innerSpreadEmpty = [1, 2, ...[...[,,,]]]

?

Works just fine.

It basically catches [...[1, 2]] and turns it into [1, 2] rather than calling the helper.

TypeScript Bot (@typescript-bot) test this

Heya Ron Buckton (@rbuckton), I've started to run the extended test suite on this PR at d6b3a11. You can monitor the build here. It should now contribute to this PR's status checks.

Verified that the only differences in our RWC suite are expected.

Sheetal Nandi (sheetalkamat) reviewed Apr 29, 2019

View reviewed changes

Comment thread src/compiler/factory.ts

Ron Buckton (rbuckton) force-pushed the spreadArraysES5 branch from 528601f to a451953 Compare April 29, 2019 23:45

Ron Buckton (rbuckton) requested a review from Wesley Wigham (weswigham) April 30, 2019 00:10

Ron Buckton (rbuckton) marked this pull request as ready for review April 30, 2019 00:10

Ryan Cavanaugh (RyanCavanaugh) assigned Ron Buckton (rbuckton) Apr 30, 2019

Add __spreadArrays helper

66323c2

Ron Buckton (rbuckton) force-pushed the spreadArraysES5 branch from a451953 to 66323c2 Compare May 2, 2019 18:11

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request May 10, 2019

Design Meeting Notes, 5/10/2019 #31350

Closed

Daniel Rosenwasser (DanielRosenwasser) added this to the TypeScript 3.6.0 milestone May 15, 2019

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request May 29, 2019

TypeScript 3.6 Iteration Plan #31639

Closed

Ron Buckton (rbuckton) mentioned this pull request Jun 3, 2019

Add '__spreadArrays' helper microsoft/tslib#67

Merged

Wesley Wigham (weswigham) reviewed Jun 10, 2019

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Wesley Wigham (weswigham) approved these changes Jun 10, 2019

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Merge branch 'master' into spreadArraysES5

d6b3a11

Ron Buckton (rbuckton) merged commit 375487e into master Jun 11, 2019

Ron Buckton (rbuckton) deleted the spreadArraysES5 branch June 11, 2019 21:16

Schalk (shelakel) mentioned this pull request Sep 3, 2019

[Bug Report] TypeScript transpilation support for es5 target for IE 10/11 compatibility vuetifyjs/vuetify#8601

Closed

KirillMetrik mentioned this pull request Sep 23, 2019

__spreadArrays throws 'Cannot read property 'length' of null' when --strictNullChecks is off #33549

Closed

Paul (devpaul) mentioned this pull request Dec 11, 2019

Update tslib to 1.10 theintern/intern#1003

Closed

HarkaranGill mentioned this pull request May 29, 2020

Typescript errors: cannot read property 'length' of undefined for spread operator, incompatibility from 3.5.1 to 3.6.3 #38855

Closed

James Hartig (jameshartig) mentioned this pull request Jun 7, 2023

switch to Array.from rather than spread operator IABTechLab/iabgpp-es#27

Merged

Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025

                       }
+                      function isPackedElement(node: Expression) {
+                          return !isOmittedExpression(node);

Add __spreadArrays helper by rbuckton · Pull Request #31166 · microsoft/TypeScript · GitHub

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Add __spreadArrays helper - #31166

Add __spreadArrays helper#31166Ron Buckton (rbuckton) merged 2 commits intomastermicrosoft/TypeScript:masterfrom spreadArraysES5microsoft/TypeScript:spreadArraysES5Copy head branch name to clipboard

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Add __spreadArrays helper#31166
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