How to use the vega-dataflow.Node function in vega-dataflow

function domEvent(sig, selector, exp, spec) {
    var evt = selector.event,
        name = selector.name,
        mark = selector.mark,
        target   = selector.target,
        filters  = dl.array(selector.filters),
        registry = target ? external : internal,
        type = target ? target+':'+evt : evt,
        node = registry.nodes[type] || (registry.nodes[type] = new df.Node(model)),
        handlers = registry.handlers[type] || (registry.handlers[type] = []);

    if (name) {
      filters.push('!!event.vg.name["' + name + '"]'); // Mimic event bubbling
    } else if (mark) {
      filters.push('event.vg.item.mark && event.vg.item.mark.marktype==='+dl.str(mark));
    }

    handlers.push({
      signal: sig,
      exp: exp,
      spec: spec,
      filters: filters.map(function(f) { return model.expr(f); })
    });

    node.addListener(sig);

prototype.model = function(model) {
  if (!arguments.length) return this._model;
  if (this._model !== model) {
    this._model = model;
    this._streamer = new df.Node(model);
    this._streamer._rank = -1;  // HACK: To reduce re-ranking churn.
    this._changeset = df.ChangeSet.create();
    if (this._handler) this._handler.model(model);
  }
  return this;
};

global.viewFactory = function(model) {
  model.scene(new Node(model)).fire();
  return model;
};

function build() {
  var v = this;
  v._renderNode = new df.Node(v._model)
    .router(true);

  v._renderNode.evaluate = function(input) {
    log.debug(input, ['rendering']);

    var s = v._model.scene(),
        h = v._handler;

    if (h && h.scene) h.scene(s);

    if (input.trans) {
      input.trans.start(function(items) { v._renderer.render(s, items); });
    } else if (v._repaint) {
      v._renderer.render(s);
    } else if (input.dirty.length) {
      v._renderer.render(s, input.dirty);