Run results for: startsWith vs include vs substring

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0) Gecko/20100101 Firefox/78.0

Browser: Firefox 78

Operating system: Mac OS X 10.14

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
JS startsWith	2255.2 Ops/sec
JS includes	1405.9 Ops/sec
JS substring	1325.3 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; })

Run results for: startsWith vs include vs substring

JS startsWith

JS includes

JS substring