get frame rate using requestAnimationFrame and promises

getFrameRate.js

function getFrameRate(ms) {
  var i = -1
  var run = true
  function tick() {
    if (run === false) {return}
    i++
    window.requestAnimationFrame(tick)
  }
  
  return new Promise(function(resolve){
    tick()
    setTimeout(function(){
      run = false
      resolve( (i/ms) * 1000 )
    }, ms)
  })
}

// usage

getFrameRate(1000).then(function(res){
  console.log(res)
  console.log(res === 60)
})