src/menu.js
function setClass(dom, cls, on) {
  if (on) dom.classList.add(cls)
  else dom.classList.remove(cls)
}
function setClass(dom, cls, on) {
  if (on) dom.classList.add(cls)
  else dom.classList.remove(cls)
}
function setClass ( dom , cls , on ) { if ( on ) dom . classList . add ( cls ) else dom . classList . remove ( cls ) }
Work around classList.toggle being broken in IE11
Work around classList . toggle being broken in IE11