function (el, check) {
  var cls = el.classList
  var size = cls.length
  var result = false
  var i = 0
  for (i; i < size; i++) {
    if (cls[i].toString() === check) result = true
  }
  return result
}
function (el, check) {
  var cls = el.classList
  var size = cls.length
  var result = false
  var i = 0
  for (i; i < size; i++) {
    if (cls[i].toString() === check) result = true
  }
  return result
}
function ( el , check ) { var cls = el . classList var size = cls . length var result = false var i = 0 for ( i ; i < size ; i ++ ) { if ( cls [ i ] . toString ( ) === check ) result = true } return result }
return number
- check element class
return number - check element class