JSFiddle - React, Tailwind, and code Playground

HTML

<div id="myDiv"></div>
<div><button type="button" onclick="Add();">Add</button></div>
<div><button type="button" onclick="Check();">Check</button></div>

JavaScript

var dynamicContentId = "DynamicDiv";
function Add() {
    if ($("#" + dynamicContentId).length == 0) {
        $("#myDiv").append("<div id=\"" + dynamicContentId + "\">hello world</div>");
    }
    else {
        alert("already added");
    }
}

function Check() {
    if ($("#" + dynamicContentId).length > 0)
        alert("exists");
    else
        alert("doesn't exist");
}