Как скрыть блок div после выполнения формы?

var form = document.getElementById("form"); 
var result = document.getElementById("result"); 
function getResult() { 
  form.classList.add("hidden"); 
  result.classList.remove("hidden"); 
}

.hidden { 
  display: none; 
}

<div id="form"> 
  <form id="paypal" name="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" target="iframe name"> 
    <input type="hidden" name="charset" value="utf-8"> 
    <input type="hidden" name="cmd" value="_xclick"> 
    <input type="hidden" name="item_number" value="funds01"> 
    <input type="hidden" name="item_name" value="Deposit"> 
    <input type="hidden" name="quantity" value="1"> 
    <input type="hidden" name="custom" value="admin"> 
    <input type="hidden" name="receiver_email" value="example@yandex.ru"> 
    <input type="hidden" name="business" value="example@yandex.ru"> 
    <input type="hidden" name="no_shipping" value="1"> 
    <input type="hidden" name="currency_code" value="USD"> 
    <input type="hidden" name="no_note" value="1"> 
    <input type="text" class="form-control" name="amount"> 
    <button type="submit" onclick="getResult()">Go to payment</button> 
  </form> 
</div> 
 
<div id="result" class="hidden"> 
  <iframe name="iframe name"></iframe> 
</div>

var form = document.getElementById("form"); 
var result = document.getElementById("result"); 
 
function getResult() { 
  var xhr = new XMLHttpRequest(); 
 
  xhr.open("POST", 'https://www.paypal.com/cgi-bin/webscr', true); 
 
  xhr.onreadystatechange = function() { 
    if (xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200 || 302) { 
      form.classList.add("hidden"); 
      result.classList.remove("hidden"); 
    }; 
  }; 
 
  xhr.send(); 
}

.hidden { 
  display: none; 
}

<div id="form"> 
  <form id="paypal" name="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" target="iframe name"> 
    <input type="hidden" name="charset" value="utf-8"> 
    <input type="hidden" name="cmd" value="_xclick"> 
    <input type="hidden" name="item_number" value="funds01"> 
    <input type="hidden" name="item_name" value="Deposit"> 
    <input type="hidden" name="quantity" value="1"> 
    <input type="hidden" name="custom" value="admin"> 
    <input type="hidden" name="receiver_email" value="example@yandex.ru"> 
    <input type="hidden" name="business" value="example@yandex.ru"> 
    <input type="hidden" name="no_shipping" value="1"> 
    <input type="hidden" name="currency_code" value="USD"> 
    <input type="hidden" name="no_note" value="1"> 
    <input type="text" class="form-control" name="amount"> 
    <button type="submit" onclick="getResult()">Go to payment</button> 
  </form> 
</div> 
 
<div id="result" class="hidden"> 
  <iframe name="iframe name"></iframe> 
</div>

document.querySelector('button').addEventListener('click', function() { 
  document.querySelector('#result').style.display = 'block'; 
  document.querySelector('#form').style.display = 'none'; 
})

#result { 
  display: none; 
}

<div id="form"> 
  <form id="paypal" name="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" target="iframe name"> 
 
    <input type="text" class="form-control" name="amount"> 
    <button type="submit">Go to payment</button> 
  </form> 
</div> 
 
<div id="result"> 
  <iframe name="iframe name"></iframe> 
</div>

$('#paypal').submit(function(){  
 $.ajax({ 
  type: 'POST', 
  url: 'https://www.paypal.com/cgi-bin/webscr', 
  data: 'параметры', 
  complete: function(){ 
    $('#paypal').hide() 
    $('#result').hide() 
  } 
}); 
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
<div id="form"> 
  <form id="paypal" name="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" target="iframe name"> 
    <input type="hidden" name="charset" value="utf-8"> 
    <input type="hidden" name="cmd" value="_xclick"> 
    <input type="hidden" name="item_number" value="funds01"> 
    <input type="hidden" name="item_name" value="Deposit"> 
    <input type="hidden" name="quantity" value="1"> 
    <input type="hidden" name="custom" value="admin"> 
    <input type="hidden" name="receiver_email" value="example@yandex.ru"> 
    <input type="hidden" name="business" value="example@yandex.ru"> 
    <input type="hidden" name="no_shipping" value="1"> 
    <input type="hidden" name="currency_code" value="USD"> 
    <input type="hidden" name="no_note" value="1"> 
    <input type="text" class="form-control" name="amount"> 
    <button type="submit">Go to payment</button> 
  </form> 
</div> 
 
<div id="result"> 
  <iframe name="iframe name"></iframe> 
</div>