JSFiddle - React, Tailwind, and code Playground

HTML

<div class="form-group">
    1 <input type="checkbox" name="checkers" /> <br />
    2 <input type="checkbox" name="checkers" /> <br />
    3 <input type="checkbox" name="checkers" /> <br />
    4 <input type="checkbox" name="checkers" />
</div>

<div class="form-group">
    Remove User? <input type="checkbox" id="remove-user" />
</div>

<div class="form-group">
    Selected Count: <span class="amount"></span>
</div>

JavaScript

/*
    Lines 5-10 will probably only work properly if this is written at the BOTTOM of the page. Unless you put it on a $(document).ready(function() { .. } );
*/
var length;
length = $('input[type="checkbox"]:checked').length;
if ( length === 0 ) {
    $('#remove-user').addClass('disabled');   
} else {
    $('#remove-user').removeClass('disabled');
}

// Each time a checkbox is clicked it'll run this check
$('input[type="checkbox"]').click(function() {
    var length;
    length = $('input[type="checkbox"]:checked').length;
    $('.amount').text(length);
    if ( length === 0 ) {
        $('#remove-user').addClass('disabled');   
    } else {
        $('#remove-user').removeClass('disabled');
    }
});