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doc: add explanation why keep var with for loop in async_hooks #30380

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doc: add explanation why keep var with for loop in async_hooks #30380

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lrecknagel
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@lrecknagel lrecknagel commented Nov 12, 2019 •
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Refs: nceu19-async_hooks

This comment will help contributors to understand why keeping var in some for loop instead changing at to let, as discussed with @mcollina

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • documentation is changed or added
  • commit message follows commit guidelines

@lrecknagel
doc: add explanation why keep var with for loop
0e1a18c 
Refs: nceu19-async_hooks

This comment will help contributors to understand why keeping var
@nodejs-github-bot nodejs-github-bot added the async_hooks Issues and PRs related to the async hooks subsystem. label Nov 12, 2019
@Trott
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Trott commented Nov 12, 2019

Welcome, @lrecknagel and thanks for the pull request. I'm guessing this is from a Code + Learn event. I'm not sure the "let inside a loop is much slower than var" thing is true anymore in current V8. /ping @nodejs/v8

@mcollina
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This is an extremely tight loop in a code path that is hit a lot.
This is still true on Node 10 and it would mean that we would not be able to backport this change.
Given that this is a cosmetic change that might cause issues, I prefer to not change them.

mcollina
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LGTM

@jasnell jasnell added the code-and-learn Issues related to the Code-and-Learn events and PRs submitted during the events. label Nov 12, 2019
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Trott commented Nov 12, 2019

This is an extremely tight loop in a code path that is hit a lot.
This is still true on Node 10 and it would mean that we would not be able to backport this change.
Given that this is a cosmetic change that might cause issues, I prefer to not change them.

Cool. Let's see if we can get that information into the comment. As it reads now, it could encourage someone to go through and change all let in loops to var throughout core.

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Trott commented Nov 12, 2019

I left two optional suggestions. It will save someone a little bit of git blame archaeology should these lines get moved around, edited, etc. But totally optional. Thanks.

@mscdex mscdex mentioned this pull request Nov 13, 2019
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CI: https://ci.nodejs.org/job/node-test-pull-request/26587/

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CI: https://ci.nodejs.org/job/node-test-pull-request/27032/

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the windows failure sequential/test-inspector-contexts is known as in #30519

the windows failure parallel/test-inspector-wait-for-connection is known as in #30619

the linux containerized failure parallel/test-readline-async-iterators-destroy is reported #30660

gireeshpunathil pushed a commit that referenced this pull request Nov 26, 2019
@lrecknagel @gireeshpunathil
doc: add explanation why keep var with for loop
4506991 
This comment will help contributors to understand why keeping var
PR-URL: #30380
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
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landed in 4506991

addaleax pushed a commit that referenced this pull request Nov 30, 2019
@lrecknagel @addaleax
doc: add explanation why keep var with for loop
329a821 
This comment will help contributors to understand why keeping var
PR-URL: #30380
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
targos pushed a commit that referenced this pull request Dec 1, 2019
@lrecknagel @targos
doc: add explanation why keep var with for loop
5be20b4 
This comment will help contributors to understand why keeping var
PR-URL: #30380
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
@BridgeAR BridgeAR mentioned this pull request Dec 3, 2019
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@BethGriggs BethGriggs mentioned this pull request Dec 9, 2019
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MylesBorins pushed a commit that referenced this pull request Dec 17, 2019
@lrecknagel @MylesBorins
doc: add explanation why keep var with for loop
c705a8e 
This comment will help contributors to understand why keeping var
PR-URL: #30380
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
@BethGriggs BethGriggs mentioned this pull request Dec 23, 2019
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@Fdawgs Fdawgs mentioned this pull request Mar 1, 2021
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Aschen commented Jul 18, 2022

👋 Just passing by here and I was curious so I ran some benchmarks if anyone is curious about this.

At the time of Node.js 6 it was a real performance gain but nowadays it's almost the same

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@github-actions github-actions bot mentioned this pull request Apr 24, 2024
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@gireeshpunathil gireeshpunathil gireeshpunathil approved these changes

@jasnell jasnell jasnell approved these changes

@mcollina mcollina mcollina approved these changes

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@lrecknagel @Trott @mcollina @nodejs-github-bot @gireeshpunathil @Aschen @jasnell