JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="categories">
    <li data-category="category-1">Category 1</li>
    <li data-category="category-1">Category 1</li>
    <li data-category="category-1">Category 1</li>
    <li data-category="category-1">Category 1</li>
    <li data-category="category-1">Category 1</li>
    <li data-category="category-2">Category 2</li>
    <li data-category="category-2">Category 2</li>
    <li data-category="category-2">Category 2</li>
    <li data-category="category-3">Category 3</li>
</ul>
<div id='result'></div>

JavaScript

var iterate = 1;
$('ul.categories li').each(function (i, v) {
    var thisCat = $(v).data('category');
    if ($('div#' + thisCat).length > 0) {
        $('div#' + thisCat).text(thisCat + ' (' + ++iterate + ')');
    } else {
        iterate = 1;
        var newDiv = '<div id="' + thisCat + '">' + thisCat + ' (1)</div>';
        $('#result').append(newDiv);
    }
});