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repl: use String#repeat instead of Array#join #3900

Merged
merged 1 commit into from
Dec 21, 2015
Merged

repl: use String#repeat instead of Array#join #3900

merged 1 commit into from
Dec 21, 2015
+4 −2

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evanlucas
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String#repeat is quite a bit faster than new Array().join().

@evanlucas evanlucas added the repl Issues and PRs related to the REPL subsystem. label Nov 18, 2015
@Fishrock123
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LGTM, evidence of said perf would be nice of course.

@evanlucas
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In the common case here:

This is testing:

'  '.repeat(1)

// vs

new Array(2).join('  ')

String#repeat 14.5 ns/op
Array#join 255.3 ns/op

@cjihrig
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cjihrig commented Nov 18, 2015

LGTM. The speedup is nice. Not sure how important it is in the REPL.

@evanlucas
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The advantage is the speedup in showing the prompt IMO

@cjihrig
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cjihrig commented Nov 18, 2015

I don't think anyone will perceive < 1us :-)

It's still nice to know for more performance critical places.

@evanlucas
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yea, true

@ronkorving
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It seems that the only place where this pattern emerged is in repl.js, unless my grep is not revealing enough.

$ grep -r 'new Array(' .
./dns.js:      var args = new Array(arguments.length + 1);
./domain.js:    var args = new Array(len - 1);
./events.js:      args = new Array(len - 1);
./events.js:  var copy = new Array(i);
./fs.js:  const chunks = new Array(len);
./internal/child_process.js:  // Don't concat() a new Array() because it would be sparse, and
./net.js:    var chunks = new Array(data.length << 1);
./querystring.js:var hexTable = new Array(256);
./repl.js:    var levelInd = new Array(this.lines.level.length).join('..');
./repl.js:    self.lines.push(new Array(self.lines.level.length).join('  ') + cmd);
./timers.js:      var args = new Array(length - 2);
./timers.js:      var args = new Array(length - 2);
./timers.js:      args = new Array(len - 1);
./util.js:  var output = new Array(value.length);

silverwind
silverwind reviewed Dec 21, 2015
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lib/repl.js
var levelInd = new Array(this.lines.level.length).join('..');
const len = this.lines.level.length
? this.lines.level.length - 1
: 0;
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This could fit on a single line.

@silverwind
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LGTM with style nit. By the way: https://jsperf.com/string-repeat-native-vs-array-join-vs-loop

@evanlucas
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Fixed the nit

CI: https://ci.nodejs.org/job/node-test-pull-request/1038/

silverwind
silverwind reviewed Dec 21, 2015
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lib/repl.js
self.lines.push(new Array(self.lines.level.length).join(' ') + cmd);
const len = self.lines.level.length
? self.lines.level.length - 1
: 0;
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Please this one too :)

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ahh missed that one. Fixed

@silverwind
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CI is happy, let's land it!

@evanlucas
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k, landing now

@evanlucas
repl: use String#repeat instead of Array#join
50125e2 
String#repeat is quite a bit faster than new Array().join().

PR-URL: nodejs#3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
@evanlucas evanlucas closed this Dec 21, 2015
@evanlucas evanlucas deleted the stringrepeat branch December 21, 2015 17:00
@evanlucas evanlucas merged commit 50125e2 into nodejs:master Dec 21, 2015
@evanlucas
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Landed in 50125e2. Thanks!

Fishrock123 pushed a commit to Fishrock123/node that referenced this pull request Dec 22, 2015
@evanlucas @Fishrock123
repl: use String#repeat instead of Array#join
09c9110 
String#repeat is quite a bit faster than new Array().join().

PR-URL: nodejs#3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Fishrock123 pushed a commit to Fishrock123/node that referenced this pull request Jan 6, 2016
@evanlucas @Fishrock123
repl: use String#repeat instead of Array#join
d11930d 
String#repeat is quite a bit faster than new Array().join().

PR-URL: nodejs#3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
MylesBorins pushed a commit that referenced this pull request Jan 13, 2016
@evanlucas
repl: use String#repeat instead of Array#join
dbf6537 
String#repeat is quite a bit faster than new Array().join().

PR-URL: #3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
MylesBorins pushed a commit that referenced this pull request Jan 19, 2016
@evanlucas
repl: use String#repeat instead of Array#join
9855fab 
String#repeat is quite a bit faster than new Array().join().

PR-URL: #3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
@MylesBorins MylesBorins mentioned this pull request Jan 19, 2016
Merged
scovetta pushed a commit to scovetta/node that referenced this pull request Apr 2, 2016
@evanlucas
repl: use String#repeat instead of Array#join
d260d0c 
String#repeat is quite a bit faster than new Array().join().

PR-URL: nodejs#3900
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
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7 participants
@evanlucas @Fishrock123 @cjihrig @ronkorving @silverwind @jasnell @MylesBorins