JSFiddle - React, Tailwind, and code Playground

HTML

<table id="add">
    <tr><td>Content_1</td></tr>
    <tr><td>Content_End</td><td><button onclick="Javascript:return addrow()">+</button></td></tr>
</table>
<button onclick="Javascript:return doTheInsert()">+</button>

JavaScript

var num=1;
function addrow(){

var table = document.getElementById("add");
var row = table.insertRow(num);
var cell1 = row.insertCell(0);
var cell2 = row.insertCell(1);

cell1.innerHTML = "NEW CELL"+num;
cell2.innerHTML = "NEW CELL"+num;
cell2.innerHTML = ""
    num++;
}