JSFiddle - React, Tailwind, and code Playground

HTML

<div class="TEST">100</div>
<div  class="TEST">1000</div>
<div  class="TEST">1500</div>
<div  class="TEST">2000</div>
<div  class="TEST">2700</div>
<div  class="TEST">3870</div>
<div  class="TEST">12040</div>

JavaScript

$('.TEST').each(function() {
num = $(this).html();
if(num > 999) {num = parseInt(num)/parseInt(1000);
num = num.toFixed(1).replace(/\.0$/, '') + 'K'; };
$(this).html(num);
});