Leaflet add/remove marker

<!DOCTYPE html>
<html>
  <head>
    <link data-require="leaflet@0.7.3" data-semver="0.7.3" rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.3/leaflet.css" />
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <div id="map"></div>
    <script data-require="leaflet@0.7.3" data-semver="0.7.3" src="//cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.3/leaflet.js"></script>
    <script src="script.js"></script>
  </body>
</html>

var tileLayer = new L.TileLayer('http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
  'attribution': 'Map data © <a href="http://openstreetmap.org">OpenStreetMap</a> contributors'
});

var map = new L.Map('map', {
  'center': [0,0],
  'zoom': 3,
  'layers': [tileLayer]
});

var marker;

map.on('click', function (e) {
  if (marker) {
    map.removeLayer(marker);
  }
  marker = new L.Marker(e.latlng).addTo(map);
});

html, body, #map {
  margin: 0px;
  width: 100%;
  height: 100%;
  padding: 0px;
}