JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post">
    <input type="checkbox" class="teste" id="box1" value="1" /> box1
    <input type="checkbox" class="teste" id="box2" value="2" /> box2
    <br />
    MyInput: <input type="text" id="MyInput" value="" />
    <input type="submit" id="submit" value="submit" />
</form>

JavaScript

$('#submit').click(function() {

    var values = [];
    $("checkbox").filter(":checked").each(function(i, box){
        values.push($(box).attr("id"));
    });
    
    $('#MyInput').val(values.join(","));
    
    return false; // just for the demo
});