// create a new draph;
  var graph = new DAG();

  // add some nodes
  graph.add('foo');
  graph.add('bar');
  graph.add('baz');

  // currently, no edges exist between these nodes, so lets add some

  graph.addEdge('foo', 'bar');

  // we now have an edge from 'foo' -> 'bar';

  graph.addEdge('bar', 'baz');

  // we now have an edge from 'foo' -> 'bar' -> 'baz';

  // to have the graph calculate this topSort for us, we can use the topSort
  // iterator, to build an ordered
  var vertices = [];

  graph.topsort(function(vertex, path){
    vertices.push(vertex.name);
  });

  vertices === [ 'foo', 'bar', 'baz' ];