Benchmark: En-To-Em Dash Regex

Script Preparation code:

const testString = "This – is – a –test –string – with – multiple – instances– of–the – pattern – and – some – variations – like–this –and this– ";
const regex1 = /(?<= )–(?= )|(?<! )– (?! )| –(?<! ) ?/g;
const regex2 = / (?=–)–? ?|– /g;
const regex3 = /(?<= )–(?! )|–(?= )|(?<! )– (?! )/g;
const regex4step1 = / +– +/g; // Remove cases with spaces on both sides
const regex4step2 = / +–|– +/g; // Remove extra spaces
const regex5 = / – | –|– /g;
const regex6 = / – ?|– /g;

Tests:

Option 1 (Lookarounds)
testString.replace(regex1, "—");
Option 2 (Simple Lookaround)
testString.replace(regex2, "—");
Option 3 (Clever)
testString.replace(regex3, "$1—");
Option 4 (Two-Pass)
testString.replace(regex4step1, " – ").replace(regex4step2, "—");
Option 5 (Normal)
testString.replace(regex5, "—");
Option 6 (I Am Dumb)
testString.replace(regex6, "—");

Historical Performance Data aggregated from 6 community runs

Desktop Results:

Chrome 6 runs

Option 5 (Normal)

630K/s

Option 1 (Lookarounds)

547K/s

Option 4 (Two-Pass)

397K/s

Fastest: Option 5 (Normal) (1.6x faster)

View exact numbers

✓ Option 5 (Normal): 629,864 ops/sec
• Option 1 (Lookarounds): 546,508 ops/sec
• Option 4 (Two-Pass): 397,338 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Option 1 (Lookarounds)
Option 2 (Simple Lookaround)
Option 3 (Clever)
Option 4 (Two-Pass)
Option 5 (Normal)
Option 6 (I Am Dumb)

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36

Browser/OS: Chrome 118 on Windows

View result in a separate tab

Option 5 (Normal)

1.0M/s

Option 6 (I Am Dumb)

1.0M/s

Option 2 (Simple Lookaround)

953K/s

Option 1 (Lookarounds)

549K/s

Option 3 (Clever)

481K/s

Option 4 (Two-Pass)

402K/s

View exact numbers

Test name	Executions per second
✓ Option 5 (Normal)	1,029,438 Ops/sec
Option 6 (I Am Dumb)	1,010,524 Ops/sec
Option 2 (Simple Lookaround)	953,051 Ops/sec
Option 1 (Lookarounds)	548,631 Ops/sec
Option 3 (Clever)	481,047 Ops/sec
Option 4 (Two-Pass)	401,505 Ops/sec

En-To-Em Dash Regex (version: 9)

Comparing performance of: `Option 1 (Lookarounds) vs Option 2 (Simple Lookaround) vs Option 3 (Clever) vs Option 4 (Two-Pass) vs Option 5 (Normal) vs Option 6 (I Am Dumb)`

Created: one year ago by: Registered User

Go to the latest result

Option 1 (Lookarounds)

Option 2 (Simple Lookaround)

Option 3 (Clever)

Option 4 (Two-Pass)

Option 5 (Normal)

Option 6 (I Am Dumb)

Historical Performance Data aggregated from 6 community runs

Desktop Results:

Chrome 6 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

En-To-Em Dash Regex (version: 9)

Comparing performance of: Option 1 (Lookarounds) vs Option 2 (Simple Lookaround) vs Option 3 (Clever) vs Option 4 (Two-Pass) vs Option 5 (Normal) vs Option 6 (I Am Dumb)

Created: one year ago by: Registered User

Go to the latest result

Option 1 (Lookarounds)

Option 2 (Simple Lookaround)

Option 3 (Clever)

Option 4 (Two-Pass)

Option 5 (Normal)

Option 6 (I Am Dumb)

Historical Performance Data aggregated from 6 community runs

Desktop Results:

Chrome 6 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Related benchmarks

Comparing performance of: `Option 1 (Lookarounds) vs Option 2 (Simple Lookaround) vs Option 3 (Clever) vs Option 4 (Two-Pass) vs Option 5 (Normal) vs Option 6 (I Am Dumb)`