title: Leaflet - button in a popup should refer to onclick.location but doesn't
body: <p>I'm new in programming with leaflet and would define myself still a newbie to html, javascript, etc.
  In a hobby-project I plan to collect data in a database.
  In my steps to get there I wanted to reach something before.
  What should happen:</p>
  <ul>
  <li>Click on a map</li>
  <li>A Popup will open</li>
  <li>There are categories to pick from [with buttons]</li>
  <li>After I picked a category something specific should happen (thats for later when im more expirienced)</li>
  <li>Just for now: an alert should open with my category and the latitude and longitute (of the onclick-function) should be visible</li>
  </ul>
  <p>But right now, the alert won't open anymore with the code below. Do you have any hints for me, what function I should look into, to solve my problem? Or is it even more easier, some sort of typo even?</p>
  <p>Thank you so much :)</p>
  <pre><code>function onMapClick(e) {
      newpopup
          .setLatLng(e.latlng)        
          .setContent(&quot;&lt;h4&gt;Neuen Standort hinzufügen&lt;/h4&gt; &lt;p&gt;Füge einen Standort hinzu z.B. dein Lieblingsrestaurant.&lt;/p&gt;&quot; + '&lt;button id=&quot;Restaurant&quot; ion-button class=&quot;button-action&quot; onclick=&quot;btn_action_res() + e.latlng&quot; block&gt;Restaurant&lt;/button&gt;'
              + '\n &lt;button id=&quot;Spielplatz&quot; ion-button class=&quot;button-action&quot; onclick=&quot;btn_action_spi() + e.latlng&quot; block&gt;Spielplatz&lt;/button&gt;') 
          .openOn(map);
  }
  
  function btn_action_res() {
      alert(&quot;Latitude : &quot; + e.latlng.lat + &quot;\nLongitude : &quot; + e.latlng.lng);
      }
  
  function btn_action_spi() {
      alert(&quot;Latitude : &quot; + e.latlng.lat + &quot;\nLongitude : &quot; + e.latlng.lng);
      }
  
  map.on('click', onMapClick);
  </code></pre>