title: How to get ID of layer in feature group on click
body: <p>I have a feature group containing several markers.</p>
  
  <p>And I have this code to respond to a click on any of the markers:</p>
  
  <pre><code>        sampleFeatureGroup.on("click", function(){ 
              alert(this.id);  // something like this
          });
  </code></pre>
  
  <p>I want to be able to get the id of the marker which is clicked on from within the function, however "this" refers to the feature group, so I cannot find the id of the marker clicked on, this seems like it should be easy but I can't figure it out.</p>