JavaScript reference html5 semantic tag

I'm new to JavaScript and this site. I need help with trying to toggle a div's visibility, the div is a html semantic tag ('nav') and I can't find a way to reference it.

I have searched for a good hour and have tried 'document.getElementById()' but that doesn't work unless I change the tag to ''.

My JavaScript code is as follows:

function toggle_visibility(id) {
"use strict";

var e = document.getElementById(id);

if (e.style.display === 'block') {

    e.style.display = 'none';
} else {

    e.style.display = 'block';
}}

And I'm calling it from another div in my html like this

<a href="#" onclick="toggle_visibility('nav');"><div id="mNav"></div></a>

<nav>
    <ul>
        <a href=""><li>
            Link 1
        </li></a>
        <a href=""><li>
            Link 2
        </li></a>
        <a href=""><li>
            Link 3
        </li></a>
    </ul>
</nav>