title: I want to onchange "change" just one time
body: <p>so: I've been trying to make an onchange change just one time, because i want the object appear on the screen after the first change, and stay on the screen:</p>
  <pre><code>&lt;select required name=&quot;Tamanho&quot; style=&quot;margin-top: 10px;margin-bottom: 10px;font-family: bebas_kairegular;font-size: 26px;&quot; onchange=&quot;button();&quot;&gt;
      &lt;option value=&quot;tamanho&quot; selected disabled id=&quot;tamanho&quot;&gt;Escolha um tamanho&lt;/option&gt;
      &lt;option value=&quot;P&quot;&gt;P&lt;/option&gt;
      &lt;option value=&quot;M&quot;&gt;M&lt;/option&gt;
      &lt;option value=&quot;G&quot;&gt;G&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;div id=&quot;button&quot; &gt;&lt;button type=&quot;button&quot; onclick=&quot;cartClick()&quot; style=&quot;font-size: 26px;&quot;&gt;Comprar&lt;/button&gt;&lt;/div&gt;
  </code></pre>
  <p>and used this javascript function to appear the div on the page</p>
  <pre><code>  function button() {
    var p = document.getElementById(&quot;button&quot;);
    if (p.style.display === &quot;none&quot;) {
      p.style.display = &quot;block&quot;;
    } else {
      p.style.display = &quot;none
    }
   }
  button();
  </code></pre>
  <p>I don't know what to do to have what i want.
  Help me please?</p>
  <p>Thank You!</p>