Js code for a blog

I’ve been learning and coding a blog for a while, and would just need some feedback, and probably some corrections on the js code.

Mostly, I’m not sure if I should use a transpiler when writing vanilla js.

Here is the file I’m talking about, but I will paste at least part of it below:

const lastModified = (element) => {
//there is a unique element with the class.
let date = document.lastModified.split(" ")[0]
//we don't want hour, minutes, seconds.
document.getElementsByClassName(element)[0].innerHTML = "Last updated: " + date 


const navBar = document.getElementById("navbar__ul");
const lines = document.getElementById("hamburger").children;
const h1 = document.getElementById("showcase__h1");
const hamburger=document.getElementById("hamburger");

const clickBurger = () => {
    return //just tells the engine the process is over.

hamburger.onclick = clickBurger

What this is doing

One of the codes adds classes when the user clicks on an element (hamburger).

The other function gets the date (only part of the output) of last modification of a document and writes it inside an element.

Is there anything you can notice wrong at first sight?