// Drag has ended
marker.on('dragend', function (e) {

  // Get position of dropped marker
  var latLng = e.target.getLatLng();

  // Object to hold nearest marker and distance
  var nearest = {};

  // Loop over layer which holds rest of the markers
  featureLayer.eachLayer(function(layer) {

    // Calculate distance between each marker and dropped marker
    var distance = latLng.distanceTo(layer.getLatLng());

    // Set the first as nearest
    if (!nearest.marker) {
      nearest.marker = layer;
      nearest.distance = distance;

    // If this marker is nearer, set this marker as nearest
    } else if (distance < nearest.distance) {
      nearest.marker = layer;
      nearest.distance = distance;
    }

  });

});