Edit in JSFiddle

const add = (a, b) => {
  return a + b
}

if (add(1, 1) === 2) {
  document.write('pass')
} else {
  document.write('fail')
}

try {
  document.write(add(1))
} catch (e) {
  if (e.message === 'add() requires two arguments') {
    document.write('pass')
  } else {
    document.write('fail')
  }
}