Auto updating Tree issue

Question

I have the following D3 js similar to http://mbostock.github.io/d3/talk/20111018/tree.html

I want to have the tree structure auto update based on new json sent by the server. The new json is sent every 5 seconds.

The issue is that I am not sure how to get rid of the old tree and just leave the updated tree. Currently it just draws a new tree image using d3 js under the most recent tree so very quickly there are tons of tree structures on the page. I would like to know how to remove the old tree image.

Any d3 or JavaScript input?

<style>

.node {
  cursor: pointer;
}

.node circle {
  fill: #fff;
  stroke: steelblue;
  stroke-width: 1.5px;
}

.node text {
  font: 10px sans-serif;
}

.link {
  fill: none;
  stroke: #ccc;
  stroke-width: 1.5px;
}

</style>

<script src="http://d3js.org/d3.v3.min.js"></script>

<script>
 var treeData2 = <%- JSON.stringify(treeJSON) %>;

 drawTree();

function drawTree () {


   treeData2.name = "broadcaster";

   console.log("tree data = ", treeData2);

  var margin = {top: 20, right: 120, bottom: 20, left: 120},
      width  = 960 - margin.right - margin.left,
      height = 800 - margin.top - margin.bottom;

  var i = 0,
      duration = 750,
      root;

  var tree = d3.layout.tree()
    .size([height, width]);

  var diagonal = d3.svg.diagonal()
      .projection(function(d) { return [d.y, d.x]; });

  svg = d3.select("body").append("svg")
      .style("overflow", "scroll")
      .attr("width", width + margin.right + margin.left)
      .attr("height", height + margin.top + margin.bottom)
        .append("g")
        .append("svg:g")
      .attr("class","drawarea")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

    root = treeData2;
    root.x0 = height / 2;
    root.y0 = 0;

    function collapse(d) {
      if (d.children) {
        d._children = d.children;
        d._children.forEach(collapse);
        d.children = null;
      }
    }

    root.children.forEach(collapse);
    update(root);


    var inter = setInterval(function() { 

      socket.get('/channel/13/tree', function(updatedJSON) {

        console.log("Updated Json = ", updatedJSON);
        treeData2 = updatedJSON;
      })

      drawTree();
    }, 5000);

  d3.select(self.frameElement).style("height", "800px");

  function update(source) {

    // Compute the new tree layout.
    var nodes = tree.nodes(root).reverse(),
      links = tree.links(nodes);

    // Normalize for fixed-depth.
    nodes.forEach(function(d) { d.y = d.depth * 180; });

    // Update the nodes…
    var node = svg.selectAll("g.node")
      .data(nodes, function(d) { return d.id || (d.id = ++i); });

    // Enter any new nodes at the parent's previous position.
    var nodeEnter = node.enter().append("g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + source.y0 + "," + source.x0 + ")"; })
      .on("click", click);

    nodeEnter.append("circle")
      .attr("r", 1e-6)
      .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });

    nodeEnter.append("text")
      .attr("x", function(d) { return d.children || d._children ? -10 : 10; })
      .attr("dy", ".35em")
      .attr("text-anchor", function(d) { return d.children || d._children ? "end" : "start"; })
      .text(function(d) { return d.name; })
      .style("fill-opacity", 1e-6);

    // Transition nodes to their new position.
    var nodeUpdate = node.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; });

    nodeUpdate.select("circle")
      .attr("r", 4.5)
      .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });

    nodeUpdate.select("text")
      .style("fill-opacity", 1);

    // Transition exiting nodes to the parent's new position.
    var nodeExit = node.exit().transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + source.y + "," + source.x + ")"; })
      .remove();

    nodeExit.select("circle")
      .attr("r", 1e-6);

    nodeExit.select("text")
      .style("fill-opacity", 1e-6);

    // Update the links…
    var link = svg.selectAll("path.link")
      .data(links, function(d) { return d.target.id; });

    // Enter any new links at the parent's previous position.
    link.enter().insert("path", "g")
      .attr("class", "link")
      .attr("d", function(d) {
        var o = {x: source.x0, y: source.y0};
        return diagonal({source: o, target: o});
      });

    // Transition links to their new position.
    link.transition()
      .duration(duration)
      .attr("d", diagonal);

    // Transition exiting nodes to the parent's new position.
    link.exit().transition()
      .duration(duration)
      .attr("d", function(d) {
        var o = {x: source.x, y: source.y};
        return diagonal({source: o, target: o});
      })
      .remove();

    // Stash the old positions for transition.
    nodes.forEach(function(d) {
      d.x0 = d.x;
      d.y0 = d.y;
    });

    d3.select("svg")
      .call(d3.behavior.zoom()
        .scaleExtent([0.5, 5])
        .on("zoom", zoom));


    node
        .exit()
          .remove();
    link
        .exit()
          .remove();      


  }

  // Toggle children on click.
  function click(d) {
    if (d.children) {
      d._children = d.children;
      d.children = null;
    } else {
      d.children = d._children;
      d._children = null;
    }
    update(d);
  }

  // Allows for zoom and drag properties
  function zoom() {
    var scale = d3.event.scale,
      translation = d3.event.translate,
      tbound = -height * scale,
      bbound = height * scale,
      lbound = (-width + margin.right) * scale,
      rbound = (width- margin.left) * scale;

    // limit translation to thresholds
    translation = [
      Math.max(Math.min(translation[0], rbound), lbound),
      Math.max(Math.min(translation[1], bbound), tbound)
    ];
    d3.select(".drawarea")
      .attr("transform", "translate(" + translation + ")" +
            " scale(" + scale + ")");
  }
}
</script>

Answer 1

To delete the old SVG, simply select and remove it:

d3.selectAll("svg").remove();