I edited Matty's code a bit and I got it working 
EDITED MY WHOLE POST AGAIN, SORRY 
Now I used colors instead of visibility, black when hidden en white when showing.
But Only the first div shows up now, not the second and the third on that page 
This is the code I used:
css:
code:
#spoiler{
  color: #000000;
  font-size:8pt;
}
javascript:
code:
<script>
   function hide(id){
      document.getElementById(id).style.display = 'none';
   }    
   function show(id){
      document.getElementById(id).style.display = '';
   }
   function spoilerhide(id){
      document.getElementById(id).style.color = '#000000';
   }
   function spoilershow(id){
      document.getElementById(id).style.color = '#FFFFFF';
   }
</script>
<div id="div1">
    <input type="button" onClick="hide('div1'); show('div2'); spoilershow('spoiler');" value="Laat spoilers zien">
</div>
<div id="div2" style="display:none;">
    <input type="button" onClick="show('div1'); hide('div2'); spoilerhide('spoiler');" value="Verberg spoilers">
</div>