[0] https://en.wikipedia.org/wiki/Greenspun%27s_tenth_rule

But it was fun and I learned a lot, so there is that.

It would need to be something like this, though it still doesn't automatically handle inline vs block:

document.querySelectorAll('.my-elements').forEach(function(el){el.style.display = 'block'})

And apparently there are issues even with that: https://css-tricks.com/snippets/javascript/loop-queryselecto...

    const $ = (() => {
        function listProxy(arr) {
            return new Proxy(arr, {
                set: (t, p, v, r) => {
                    for(let x of t) {
                        x[p] = v;
                    }
                },
                get: (t, p, r) => {
                    if(t.length > 0 && t[0][p] instanceof Function) {
                        return (...args) => { Array.prototype.map.call(t, (x) => x[p](args)) };
                    } else {
                        return listProxy( Array.prototype.map.call(t, (x) => x[p]) );
                    }
                }
            })
        }

        return (sel, root) => {
            if(root === undefined) root = document;
            return listProxy(root.querySelectorAll(sel));
        }
    })();

    // use like this:
    $('.my-elements').className = 'Important'; 
    $('.my-elements').style.color = 'Red';     
    $('.my-elements').classList.add('Another');

  document.querySelectorAll('.myclass')
    .forEach(el => el.style.display = 'block')

  Array.from(document.querySelectorAll('.myclass'))
    .forEach(el => el.style.display = 'block')

Just haven't taken the time... at least the main app I work on at work doesn't need to support IE11. Latest Edge,, Firefox, Safari and Chrome ... and Chrome is the primary target.

https://developer.mozilla.org/en-US/docs/Web/API/NodeList/fo...

    NodeList.prototype.forEach = Array.prototype.forEach;

    NodeList.prototype.forEach === Array.prototype.forEach

  Array.prototype.forEach.call(document.querySelectorAll('div'), console.log)

Missing:

[0]https://caniuse.com/#feat=getelementsbyclassname

Try doing this with CSS, please.

    <div class="element"></div>

    .element { display: block; }
    .element.is-hidden { display: none; }

    document.getElementsByClassName("element")[0].classList.add( "is-hidden" );