Tile URL-Function

function(coords) {
  var tile = L.DomUtil.create('canvas', 'leaflet-tile');
  var ctx = tile.getContext('2d');
  var size = this.getTileSize()
  tile.width = size.x
  tile.height = size.y
  
  // calculate projection coordinates of top left tile pixel
  var nwPoint = coords.scaleBy(size)
  
  // calculate geographic coordinates of top left tile pixel
  var nw = map.unproject(nwPoint, coords.z)
  
  // will not create white background
  //ctx.fillStyle = 'white';
  //ctx.fillRect(0, 0, size.x, 50);
  //ctx.fillStyle = 'black';

  var vx = " " + coords.x;
  var vy = " " + coords.y;

  ctx.fillText('x:' + vx.substr(1, 10) + ', y:' + vy.substr(1, 10) + ', zoom: ' + coords.z, 20, 20);

  vx = " " + nw.lat;
  vy = " " + nw.lng;

  ctx.fillText('lat:' + vx.substr(1, 10) + ', lon:' + vy.substr(1, 10), 20, 40);

  ctx.strokeStyle = 'black';
  ctx.beginPath();
  ctx.moveTo(0, 0);
  ctx.lineTo(size.x, 0);
  ctx.lineTo(size.x, size.y);
  ctx.lineTo(0, size.y);
  ctx.closePath();
  ctx.stroke();

  return tile;
}