function (el) {
  this.el = el
  if(typeof el.classList !== 'undefined') {
    // if classList support
    this.old = false
  } else {
    // browser class unsupport classList
    this.classList = new nativeClasList(el)
    this.old = true
  }
}
function (el) {
  this.el = el
  if(typeof el.classList !== 'undefined') {
    
    this.old = false
  } else {
    
    this.classList = new nativeClasList(el)
    this.old = true
  }
}
function ( el ) { this . el = el if ( typeof el . classList !== 'undefined' ) { // if classList support this . old = false } else { // browser class unsupport classList this . classList = new nativeClasList ( el ) this . old = true } }
define classList object
define classList object