JSFiddle - React, Tailwind, and code Playground

HTML

<form name="formPurchase" action="" method="POST">
    <input type="radio" name="purchaseType" value="kaas" onclick="showForm('kaas');">optie1
    <br>
    <input type="radio" name="purchaseType" value="ham" onclick="showForm('ham')">optie2
    <br>
    <input type="radio" name="purchaseType" value="pindakaas" onclick="showForm('pindakaas')">optie3
    <br>
    <br>
</form>
<form id='kaas' style="display: none;" name="formKaas" class="formKaas" action=" <?php $_SERVER['PHP_SELF'] ?>" method="POST">
    <input type="radio" name="orderKaas" value="optie11">
    <br>
    <input type="radio" name="orderKaas" value="optie12">
    <br>
    <input type="Submit" Name="continuOrder" Value="Continu">
</form>
<form id='ham' style="display: none;" name="formHam" class="formHam" action=" <?php $_SERVER['PHP_SELF'] ?>" method="POST">
    <input type="radio" name="orderHam" value="optie11">
    <br>
    <input type="radio" name="orderHam" value="optie12">
    <br>
    <input type="Submit" Name="continuOrder" Value="Continu">
</form>
<form id='pindakaas' style="display: none;" name="formPindakaas" class="formPindakaas" action=" <?php $_SERVER['PHP_SELF'] ?>" method="POST">
    <input type="radio" name="orderPindakaas" value="optie11">
    <br>
    <input type="radio" name="orderPindakaas" value="optie12">
    <br>
    <input type="Submit" Name="continuOrder" Value="Continu">
</form>

JavaScript

function showForm(selection) 
{
    // Array aanmaken
    var options = new Array('kaas', 'ham', 'pindakaas');
    // Alles verbergen
    for (i = 0, max = options.length; i < max; i++) { document.getElementById(options[i]).style.display = 'none';
    }
    // De meegegeven waarde tonen
   document.getElementById(selection).style.display = 'block';
}