JSFiddle - React, Tailwind, and code Playground

HTML

<button class="supernappula">Test</button><br>
<input value="1" class="item-quantity simpleCart_input" type="text">

JavaScript

$(".supernappula").live('click', function() {
   if( $('.item-quantity.simpleCart_input').length){
      $('.item-quantity.simpleCart_input').replaceWith(function(){
         return '<span class='+this.className+'>'+this.value+'</span>'
      }) 
    }   
});