JSFiddle - React, Tailwind, and code Playground

HTML

<table id="table">
    <tr>
        <td>2</td>
    </tr>
    <tr>
        <td>6</td>
    </tr>
    <tr>
        <td>2</td>
    </tr>
    <tr>
        <td>1</td>
    </tr>
    <tr>
        <td>1</td>
    </tr>
    <tr>
        <td>1</td>
    </tr>
</table>
<button type="button" onclick="Calcular('table')">Calcular</button>

JavaScript

Calcular = function(id){
            var table = document.getElementById(id);
            var td    = table.getElementsByTagName('td');
            var dados = {};
            for(i = 0; i < td.length; i++)
            {
                dados[td[i].innerHTML] = (dados[td[i].innerHTML] === undefined)? 1: (dados[td[i].innerHTML] + 1);                
            }
            console.log(dados);
        }