JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="cb1">Checkbox #1
<input type="checkbox" id="cb2">Checkbox #2
<input type="checkbox" id="cb3">Checkbox #3
<hr />
<input name="selectedCB">

JavaScript

$(document).ready(displayCheckbox);

CountSelectedCB = [];

function displayCheckbox(){    
    $("input:checkbox").change(function() {          
        selectedCB = [];
        notSelectedCB = [];
        
        CountSelectedCB.length = 0; // clear selected cb count
        $("input:checkbox").each(function() {
            if ($(this).is(":checked")) {
                CountSelectedCB.push($(this).attr("id"));
            }
        });
        
        $('input[name=selectedCB]').val(CountSelectedCB); 
    });
}