JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input value="1" type="checkbox" id="admin" name="admin" /><label for="admin">admin</label>
    <input value="2" type="checkbox" id="security32" name="security32" /><label for="security32">security32</label>
    <input value="4" type="checkbox" id="security64" name="security64" /><label for="security64">security64</label>
</form>
<button onclick="determineDownload();">Submit</button>
<div id="errfn"></div>

CSS

input, label, button, div {float: left;}
input, button, div {clear: left;}

JavaScript

function determineDownload() {
    var admin = document.getElementById('admin').checked ? 1 : 0,
        security32 = document.getElementById('security32').checked ? 2 : 0,
        security64 = document.getElementById('security64').checked ? 4 : 0,
        bitmask = {
            "0": "Make at least one selection",
            "1": "admin is checked",
            "2": "security32 is checked",
            "3": "admin and security32 are checked",
            "4": "security64 is checked",
            "5": "admin and security64 are checked",
            "6": "security32 and security64 are checked",
            "7": "admin and security32 and security64 are checked"
        };
    document.getElementById('errfn').innerHTML = bitmask[admin + security32 + security64];
    return false;
}