JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css">
<script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>
<textarea id="appendedInputButton" rows="5" cols="50"></textarea>

JavaScript

function getCaretPosition (elem) {

  // Initialize
  var iCaretPos = 0;

  // IE Support
  if (document.selection) {

    // Set focus on the element
    elem.focus ();

    // To get cursor position, get empty selection range
    var oSel = document.selection.createRange ();

    // Move selection start to 0 position
    oSel.moveStart ('character', -elem.value.length);

    // The caret position is selection length
    iCaretPos = oSel.text.length;
  }
  // Firefox support
  else if (elem.selectionStart || elem.selectionStart == '0')
    iCaretPos = elem.selectionStart;

  // Return results
  return (iCaretPos);
}

function setCaretPosition(elem, caretPos) {
    if(elem != null) {
        if(elem.createTextRange) {
            var range = elem.createTextRange();
            range.move('character', caretPos);
            range.select();
        }
        else {
            if(elem.selectionStart) {
                elem.focus();
                elem.setSelectionRange(caretPos, caretPos);
            }
            else
                elem.focus();
        }
    }
}

function getTags(term, callback) {
    var data = {
        tags: [
            {name: 'john', count: 1}, {name: 'michael', count: 2} 
        ]
    };
    callback(data);    
}

$(document).ready(function() {
    $("#appendedInputButton").autocomplete({
        source: function(request, response) {
            var term = request.term;
            var pos = getCaretPosition(this.element.get(0));
            var substr = term.substring(0, pos);
            var lastIndex = substr.lastIndexOf('@');
            if (lastIndex >= 0){
                var username = substr.substr(lastIndex + 1);
                if (username.length && (/^\w+$/g).test(username)){
                    getTags(username, function(data) {
                        response($.map(data.tags, function(el) {
                            return {
                                value: el.name,
                                count:...