Can't figure out the problem with the FOR loop...

const toggleList = document.getElementById('toggleList');
const listDiv = document.querySelector('.list');
const list = listDiv.querySelector('ul')
const input = document.querySelector('input.description');
const descP = document.querySelector('p.description');
const descriptionButt = document.querySelector('button.description');
const addItemIn = document.querySelector('input.addItemIn');
const addButt = document.querySelector('button.addButt');
const removeButt = document.querySelector('button.removeButt');
const listItem = document.getElementsByTagName('li');
const existing = list.children;

function addButts (li) {
  let up = document.createElement('button');
  up.className = "up";
  up.textContent = "up";
  li.appendChild(up);

  let down = document.createElement('button');
  down.className = "down";
  down.textContent = "down";
  li.appendChild(down);

  let del = document.createElement('button');
  del.className = "del";
  del.textContent = "delete";
  li.appendChild(del);

};

for (let i = 0; i < existing.length; i+= 1);{
       addButts(existing[i]);
 }


toggleList.addEventListener('click', () => {
  if (listDiv.style.display == 'none') {
    toggleList.textContent = 'Hide list';
    listDiv.style.display = 'block';
  } else {
    toggleList.textContent = 'Show list';                        
    listDiv.style.display = 'none';
  }                         
});

descriptionButt.addEventListener('click', () => {
  descP.innerHTML = input.value + ':';
});

addButt.addEventListener('click', () => {
  let ul = document.getElementsByTagName('ul')[0];
  let li = document.createElement('li');
  li.textContent = addItemIn.value;
  ul.appendChild(li);
  addButts(li);
  addItemIn.value = '';
                           });

list.addEventListener('click', (event) => {
  if (event.target.tagName === 'BUTTON' )
  { if (event.target.className === 'remove')
    {
   let li = event.target.parentNode;
   let ul = li.parentNode;
   ul.removeChild(li);
    } ;
   if (event.target.className === 'up'){
   let li = event.target.parentNode;
   let ul = li.parentNode;
   let prevLi = li.previousElementSibling;
     if (prevLi)
     {ul.insertBefore(li, prevLi);}
   }
        if (event.target.className === 'down'){
   let li = event.target.parentNode;
   let ul = li.parentNode;
   let nextLi = li.nextElementSibling;
     ul.insertBefore(nextLi, li);
      }
    }
  }
  );