Run results for: En-To-Em Dash Regex

Run details:

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: Chrome 118

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

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

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, "—");