How to add a class to the body element in javascript?

So I wanted to code a simple thing in javascript, I have a responsive navbar with the hamburger button:

<input type="checkbox" id="check" onclick="validate()">
<label for="check" class="checkbtn">
    <i class="fas fa-bars"></i>
</label>

I wanted to halt scrolling whenever the hamburger menu is active. So I wrote this javascript code:

<script type="text/javascript">
function validate() {
    var element = document.getElementByTagName("body")[0];
    if (document.getElementById('check').checked){
        element.classList.add("noscroll");
    }
}

And of course I added .noscroll{ overflow: hidden; } to the css file.

It didn’t work for some reason which I hope you guys will help me identify.

Answer

The shortest answer, hope it helps

const body = document.body;
body.classList.add("MyClass");