Undefined value for parseInt()
<p>I'm learning Javascript events, but I have a problem about the value I type in an input.</p>

<p>When I type a number, the calcul needs to be change (keyup). Same thing about the option that I choose (change).</p>

<p>But the value that I return with my paragraph (id=res) is undifined. I don't understand what it means and how to debug it.</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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<pre class="snippet-code-js lang-js prettyprint-override"><code>// Here is the Javascript for my events (keyup and change).

document.getElementById("selectDevice").addEventListener('change', change);
document.getElementById("montant").addEventListener('keyup', change);

function change(e) {
  var montant = Number.parseInt(document.getElementById("montant").value, 10);
  var selectDevice = document.getElementById("selectDevice").value;
  switch (e.target.id) {
  case 'nothing':
    var resultat = montant;
    console.log(resultat);
    break;
  case 'usd':
    var resultat = montant * 1.14;
    console.log(resultat);
    break;
  case 'eur':
    var resultat = montant * 0.82;
    console.log(resultat);
    break;
  }
  document.getElementById("res").innerHTML = resultat
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!-- Here is the HTML --&gt;

Amount: &lt;input id="montant" type="text" /&gt;
Device: 
&lt;select id="selectDevice"&gt;
  &lt;option id="nothing" value="nothing"&gt;Please choose a device&lt;/option&gt;
  &lt;option id="usd" value="eur"&gt;EUR&lt;/option&gt;
  &lt;option id="eur" value="usd"&gt;USD&lt;/option&gt;
&lt;/select&gt;
Convert amount: &lt;span id="res"&gt;&lt;/span&gt;</code></pre>
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</p>

<p>I'm speaking french, I didn't translate all my code, but if you have some questions, I'm here =)</p>

<p>If you have some solutions from the Javascript Documentation, thank you to give me the page, because I need to learn to search in the doc in order to find my solutions by myself.</p>

<p>Have a nice day =)</p>