[Plain javascript]My mouseover effect is buggy

I'm trying to achieve a mouse hover effect using Js on three <li>s.
The effect doesn't work on the first try, I have to keep hovering my mouse again and again to go back to its original string.

note: i linked the script at the right before </body>

HTML code:

<ul>
  <li data-value="// ABOUT"    ><a href="#" >// ABOUT    </a></li>
  <li data-value="// PROJECTS" ><a href='#' >// PROJECTS </a></li>
  <li data-value="// CONTACT" ><a href="#"  >// CONTACT  </a></li>
</ul>

Javascript code:

const letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

let interval = null;

document.querySelectorAll("li").forEach(li => {
  li.onmouseover = event => {
    let iteration = 0;

    clearInterval(interval);

    interval = setInterval(() => {
      event.target.innerText = event.target.innerText
        .split("")
        .map((letter, index) => {
          if (index < iteration) {
            return event.target.dataset.value[index];
          }

          return letters[Math.floor(Math.random() * 26)];
        })
        .join("");

      if (iteration >= event.target.dataset.value.length) {
        clearInterval(interval);
      }

      iteration += 1 / 3;
    }, 30);
  };
});

Solution

1- you don't need to use event.target because you only use arrow function.
2- the interval variable should be local to avoid conflicts in your multiples setInterval
3- your code remove all links -> ex <li><a href="#" >// ABOUT </a><li> by <li>// ABOUT <li>....

so, here it is... ( with some improvemnts )

const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

document.querySelectorAll('li').forEach( li_Elm => 
  {
  let interval = null
    , li_aLink = li_Elm.querySelector('a')
    , textInit = li_aLink.textContent 
    , length   = textInit.length
    ;
  li_Elm.onmouseover =_=> 
    {
    let iteration = 0;
    clearInterval(interval);
    interval = setInterval(() =>
      {
      li_aLink.textContent = Array
        .from( ({length}), (letter,index) => 
        ( index < iteration) 
                ? textInit[index]
                : letters[Math.floor(Math.random() * 26)]
        ).join('');

      if (iteration >= length)
        clearInterval(interval);

      iteration += 1 / 3;
      }
      , 30);
    };
  });

<ul>
    <li><a href="#" >// ABOUT    </a></li>
    <li><a href='#' >// PROJECTS </a></li>
    <li><a href="#" >// CONTACT  </a></li>
  </ul>