JSFiddle - React, Tailwind, and code Playground

HTML

<div class="spacer"></div>
<textarea class="textarea"></textarea>
<ul class="list">
    <li>item</li>
</ul>

CSS

.list {
    list-style: none;
    background-color: gray;
    max-width: 100px;
    display: none;
}

JavaScript

$(".textarea").bind("keypress", function (e) {
    if (String.fromCharCode(e.keyCode) == '@') {
         $(".list").show();
    } else{
         $(".list").hide();
    }
});