time_regex.js

function time(fn) {
  var s = performance.now()
  fn()
  return performance.now() - s
}

function average(array) {
  return array.reduce((prev, cur) => prev + cur, 0) / array.length
}

async function fetchText() {
  let res = await fetch(
    'https://twitter.com/justsml/status/1221830342471868416',
  )
  return res.text()
}

async function main() {
  const value = await fetchText()
  const regex = /^[^@]+@[^@]{2,}\.[^@]{2,}$/
  const time1 = []
  const time2 = []
  var T = 10000
  for (let i = 0; i < T; i++) {
    time1.push(time(() => regex.test(value)))
  }
  console.log('time1', average(time1))
  for (let i = 0; i < T; i++) {
    time2.push(time(() => /^[^@]+@[^@]{2,}\.[^@]{2,}$/.test(value)))
  }
  console.log('time2', average(time2))
}

main()