hzzzzl

function perf(fn) {
  const t1 = performance.now()
  for(let i = 0; i < 100000; i++) {
    fn()
  }
  console.log(performance.now() - t1 + ' ms')
}

ar = [...Array(10000).keys()]

function f1() {
  for (let i = 0, y = ar.length; i < y; i++) { ar[i] = ++ar[i] }
}

function f2() {
  for (let i = 0 ; i < ar.length; i++) { ar[i] = ++ar[i] }
}

perf(f1)

perf(f2)

document.body.style.transition = '30s'
document.body.style.transform = 'translateY(-100%)'

'some test string'.slice(1, -1)
// "ome test strin"

arr[i].style = (i === 13) ? 'background:red' : 'background:green'

const updatedUser = await User.findOneAndUpdate(
  { userId: userid }, 
  { $inc: { lvl: 1 } },
  { new: true }
)