JSFiddle - React, Tailwind, and code Playground

HTML

<table id="main"><tr>
    <td>1</td>
    <td>2</td>
    <td>3</td>
    <td>4</td>
</tr><tr>
    <td>5</td>
    <td>6</td>
    <td>7</td>
    <td>8</td>
</tr><tr>
    <td>9</td>
    <td>10</td>
    <td>11</td>
    <td>12</td>
</tr></table>

CSS

table {
   border: 1px solid green;  
   cellspacing: 1px;    
}
td {
 border: 1px solid green;
 padding: 3px;        
}

JavaScript

function getVal(e) {
    var targ;
    if (!e) var e = window.event;
    if (e.target) targ = e.target;
    else if (e.srcElement) targ = e.srcElement;
    if (targ.nodeType == 3) // defeat Safari bug
        targ = targ.parentNode;

    alert(targ.innerHTML);
}

onload = function() {
    var t = document.getElementById("main").getElementsByTagName("td");
    for ( var i = 0; i < t.length; i++ )
        t[i].onclick = getVal;
}