title: Javascript hide element onclick, does not work
body: <p><br>
  I created a little table in which you can click the datacells, what will trigger my Javascript to call a function. This function shows a little "formular" at the position of the clicked datacell. Now I added a button, that should hide this formular, but it does not work and I don't know why.</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;div id="movableDiv"&gt;
  &lt;form&gt;
  &lt;p&gt;Some text:&lt;/p&gt;
  &lt;input type="text" name="someText"&gt;
  &lt;p&gt;A number:&lt;/p&gt;
  &lt;input type="number" name="aNumber"&gt;
  &lt;button type="button" ="HideButton"&gt;
  Hide
  &lt;/button&gt;
  &lt;/form&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>CSS:</p>
  
  <pre><code>#movableDiv{
    background-color: lightgrey;
    position: absolute;
    visibility: hidden;
  }
  </code></pre>
  
  <p>Javascript: </p>
  
  <pre><code>document.getElementById("HideButton").onclick = hideDiv;
  function hideDiv(){
  document.getElementById("movableDiv").style.visibility = "hidden";
  }
  </code></pre>
  
  <p><a href="https://jsfiddle.net/qc1dng63/2/" rel="nofollow noreferrer">https://jsfiddle.net/qc1dng63/2/</a></p>