JSFiddle - React, Tailwind, and code Playground

HTML

<div id="campaignTags">
    <div class="tags">Tag 1</div>
    <div class="tags">Tag 2</div>
    <div class="tags">Tag 3</div>
</div>
<label>Enter a tag: <input id="tag" /></label>

JavaScript

var $container = $('#campaignTags'),
    $template  = $('<div class="tags">'),
    tagsUsed   = {};
$.each($container.children(), function(_, el) {
    tagsUsed[el.innerText || el.textContent] = true;
});

$('#tag').keyup(function(e) {
    if (e.which === 13) {
        var tag = $.trim(this.value);
        if (! tagsUsed[tag]) {
            $template.clone().text(tag).appendTo($container);
            tagsUsed[tag] = true;
        }
    }
});