Run results for: startsWith vs include vs substring

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.1.1 Safari/605.1.15

Browser: Safari 18

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: one year ago

JS startsWith

18K/s

JS substring

13K/s

JS includes

10K/s

View exact numbers

Test name	Executions per second
✓ JS startsWith	17,669 Ops/sec
JS substring	12,973 Ops/sec
JS includes	9,788 Ops/sec

Script Preparation code:

window.prefix = "%%SOME_PREFIX%%";
const possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

function getRandomInt(max) {
  return Math.floor(Math.random() * max);
}

function makeRandomString(len) {
  var text = "";
  for( var i=0; i < len; i++ ) {
    text += possible.charAt(getRandomInt(possible.length));
  }
  return text;
}

window.allStrings = [];
for (let i = 0; i < 1000; i++) {
	allStrings.push(window.prefix + makeRandomString(1000));
	allStrings.push(makeRandomString(1000));
}

Tests:

JS startsWith
window.allStrings.forEach(s => { s.startsWith(window.prefix); })
JS includes
window.allStrings.forEach(s => { s.includes(window.prefix); })
JS substring
window.allStrings.forEach(s => { s.substring(0, window.prefix.length) === window.prefix; })