これを試してください(うまくいくといいのですが):
// mixin (functionality) for toggle class
function hasClass(ele, clsName) {
var el = ele.className;
el = el.split(' ');
if(el.indexOf(clsName) > -1){
var cIndex = el.indexOf(clsName);
el.splice(cIndex, 1);
ele.className = " ";
el.forEach(function(item, index){
ele.className += " " + item;
})
}
else {
el.push(clsName);
ele.className = " ";
el.forEach(function(item, index){
ele.className += " " + item;
})
}
}
// get all DOM element that we need for interactivity.
var btnNavbar = document.getElementsByClassName('btn-navbar')[0];
var containerFluid = document.querySelector('.container-fluid:first');
var menu = document.getElementById('menu');
// on button click job
btnNavbar.addEventListener('click', function(){
hasClass(containerFluid, 'menu-hidden');
hasClass(menu, 'hidden-phone');
})`enter code here`