JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="holder" style="width: 512px;">
    <li id="pt_5uZqW99dmlgmiuCTJiPHDC9T9o2sfz0I" rel="[email protected]" class="bit-box"><a href="#" class="closebutton">[email protected]</a></li>
    <li id="pt_9O0pMJDhtNbRgU1vNM8He8Vh9zpJ1tcE" rel="[email protected]" class="bit-box"><a href="#" class="closebutton">[email protected]</a></li>
    <li id="pt_U8JH5E9y5w4atm4CadEPvuu3wdh3WcBx" rel="[email protected]" class="bit-box"><a href="#" class="closebutton">[email protected]</a></li>
    <li id="Project_update_user_id_annoninput" 
     class="bit-input">
     <input type="text" autocomplete="off" size="0" class="maininput"></li>
    </ul>


<input id="removeuser" value="" />

JavaScript

jQuery(document).ready(function() {
        jQuery("a.closebutton").click(function(a) {
            var v = jQuery(this).parent().attr('rel');
            var t = jQuery("input#removeuser").val();
            if (t.indexOf(v) < 0) {
                if(t.length>0){
                    t += ",";
                }
                jQuery("input#removeuser").val(t + v);
            }
        });
    });