Hide all elements with class using plain Javascript

There are many ways to hide all elements which has certain class in javascript one way is to using for loop but here i want to show you other ways to doing it.

1.forEach and querySelectorAll('.classname')

document.querySelectorAll('.classname').forEach(function(el) {
   el.style.display = 'none';
});

2.for...of with getElementsByClassName

for (let element of document.getElementsByClassName("classname")){
   element.style.display="none";
}

3.Array.protoype.forEach getElementsByClassName

Array.prototype.forEach.call(document.getElementsByClassName("classname"), function(el) {
    el.style.display = 'none';
});

4.[ ].forEach and getElementsByClassName

[].forEach.call(document.getElementsByClassName("classname"), function (el) {
    el.style.display = 'none';
});

i have shown some of the possible ways, there are also more ways to do it, but from above list you can Pick whichever suits and easy for you.

Note: all above methods are supported in modern browsers but may be some of them will not work in old age browsers like internet explorer.

In the absence of jQuery, I would use something like this:

<script>
    var divsToHide = document.getElementsByClassName("classname"); //divsToHide is an array
    for(var i = 0; i < divsToHide.length; i++){
        divsToHide[i].style.visibility = "hidden"; // or
        divsToHide[i].style.display = "none"; // depending on what you're doing
    }
<script>

This is taken from this SO question: Hide div by class id, however seeing that you're asking for "old-school" JS solution, I believe that getElementsByClassName is only supported by modern browsers

Late answer, but I found out that this is the simplest solution (if you don't use jQuery):

var myClasses = document.querySelectorAll('.my-class'),
    i = 0,
    l = myClasses.length;

for (i; i < l; i++) {
    myClasses[i].style.display = 'none';
}

Demo