JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li><input type="checkbox" id="id1"/></li>
    <li><input type="checkbox" id="id2"/></li>
    <li><input type="checkbox" id="id3"/></li>
    <li><input type="checkbox" id="id4"/></li>
</ul>

<input type="button" value="calc" onclick="alert(calc())">

JavaScript

function calc(){
    var q = ""
    $("input[type=checkbox]:checked").each(function(){
        if (q != "") q += "&"
        q+= " champion = '" + $(this).attr("id") + "'"
    })
    return "var myString = \"" + q + "\"";
}