graph.js.tmpl

    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
    <script src="//d3js.org/d3.v5.min.js"></script>
    <script src="https://unpkg.com/viz.js@1.8.1/viz.js" type="application/javascript"></script>
    <script src="https://unpkg.com/d3-graphviz@2.6.0/build/d3-graphviz.min.js"></script>

    <script>
    var transition = d3.transition("t")
                       .duration(500)
                       .ease(d3.easeLinear);

    var graphviz = d3.select("#graph").graphviz(false);

    function render() {
      var graph_data = $.ajax({
        url: "http://" + controller_addr + "/simple_graph",
        dataType: "text",
        success: function(data) {
          $("#error-msg").removeClass("show");
          graphviz.transition(transition).renderDot(data);
        },
        error: function(e) {
          $("#error-msg").html("AJAX request to controller API failed: " + e.statusText).addClass("show");
          graphviz.transition(transition).renderDot('digraph {}');
        }
      });

    }

    setInterval(function() {
      render();
    }, 1000);
    </script>