JSFiddle - React, Tailwind, and code Playground

HTML

<div class='force'>
    1
</div>
<div class='force'>
    2
</div>
<div class='force'>
    3
</div>
total:
<div id='total_forces'>
    
</div>

JavaScript

(function($) {
	$.fn.sumHTML = function() {
    var sum = 0;
    this.each(function() {
      var num = parseInt($(this).html(), 10);
      sum += (num || 0);
    });
    return sum;
  };
})(jQuery);

$('#total_forces').text($('.force').sumHTML());