function (el, callback) {
  var size = el.length
  var i = 0
  for (i; i < size; i++) {
    callback(el[i], i)
  }
}
function (el, callback) {
  var size = el.length
  var i = 0
  for (i; i < size; i++) {
    callback(el[i], i)
  }
}
function ( el , callback ) { var size = el . length var i = 0 for ( i ; i < size ; i ++ ) { callback ( el [ i ] , i ) } }
(el →  dom, callback → function)
- looping querySelectorAll
( el → dom callback → function ) - looping querySelectorAll