jQuery addClass example

Change class name on click in jQuery

HTML

<div>
  <span class="ms2_total_cost">1001</span><br>
  <button class="btn btn-yellow btn-lg ms2_link">Button</button><br>
  <button id = 'testDomEvent'>Test</button>
</div>

JavaScript

var $total_cost = $('span.ms2_total_cost');

$total_cost.on('DOMSubtreeModified',function(){
  $total_cost =  $('span.ms2_total_cost').html()
  $total_cost = Number.parseInt($total_cost);

  if ($total_cost <= 1000) {
    $('button.btn.btn-yellow.btn-lg.ms2_link').prop('disabled', true);
  } else {
    $('button.btn.btn-yellow.btn-lg.ms2_link').removeAttr("disabled");
  }
 })
 
 document.querySelector('#testDomEvent').addEventListener('click', () => {
   document.querySelector('span.ms2_total_cost').textContent = Math.floor(Math.random() * 2000)
 });