app.js

const nav = document.getElementById('main__nav')
const hamburger = document.getElementById('hamburger')

nav.addEventListener('click', handleNav)
hamburger.addEventListener('click', handleNav)

function handleNav() {
  if(!nav.classList.contains('main__nav--active')){
    nav.classList.add('main__nav--active');
    hamburger.classList.add('hamburger--active')
  } else{
    nav.classList.remove('main__nav--active');
    hamburger.classList.remove('hamburger--active');
  }
}