JSFiddle - React, Tailwind, and code Playground

HTML

<form method="POST" id="subscribeForm">
    <fieldset id="cbgroup">
        <div><input name="list" id="list0" type="checkbox"  value="newsletter0" >zero</div>
        <div><input name="list" id="list1" type="checkbox"  value="newsletter1" >one</div>
        <div><input name="list" id="list2" type="checkbox"  value="newsletter2" >two</div>
    </fieldset>
    <input name="submit" type="submit"  value="submit">
</form>

JavaScript

function onSubmit() 
{ 
  var fields = $("input[name='list']").serializeArray(); 
  if (fields.length >= 2) 
  { 
    alert('nothing selected'); 
    // cancel submit
    return false;
  } 
  else 
  { 
    alert(fields.length + " items selected"); 
  }
}

// register event on form, not submit button
$('#subscribeForm').submit(onSubmit)