title: How to get coordinates of an svg element?
body: <p>I am using d3 to draw a line from a relative svg position and hence want to access the coordinates of the element itself. I tried something like this (where "this" refers to the element)</p>
  
  <pre><code> .attr("x1", this.x)
   .attr("y1", this.y)
  </code></pre>
  
  <p>but the x1 and y1 just defaults to zero. What is the correct way to get the coordinates of the svg element?</p>
  
  <p>EDIT: </p>
  
  <p>Here's my (by request) my whole code. I'm trying to implement this on the collapsible tree, where I draw a line when I hover with the mouse over a circle node. The starting point of the line should be from the circle I click on and the ending point should be a fixed point on the svg plane.</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
      &lt;meta http-equiv="Content-Type" content="text/html;charset=utf-8"&gt;
      &lt;script type="text/javascript" src="d3.v3.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="d3.layout.js"&gt;&lt;/script&gt;
      &lt;style type="text/css"&gt;
  
  .node circle {
    cursor: pointer;
    fill: #fff;
    stroke: steelblue;
    stroke-width: 1.5px;
  }
  
  .node text {
    font: 10px sans-serif;
  }
  
  path.link {
    fill: none;
    stroke: #ccc;
    stroke-width: 1.5px;
  }
  
      &lt;/style&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;div id="chart"&gt;&lt;/div&gt;
      &lt;script type="text/javascript"&gt;
  
  var m = [20, 120, 20, 120],
      w = 2240 - m[1] - m[3],
      h = 800 - m[0] - m[2],
      i = 0,
      duration = 500,
      root;
  
  var tree = d3.layout.tree()
      .size([h, w]);
  
  var diagonal = d3.svg.diagonal()
      .projection(function(d) { return [d.y, d.x]; });
  
  var vis = d3.select("#chart").append("svg")
      .attr("width", w + m[1] + m[3])
      .attr("height", h + m[0] + m[2])
    .append("g")
      .attr("transform", "translate(" + m[3] + "," + m[0] + ")");
  
  function loadData(json) {
      root = json;
      d3.select("#processName").html(root.text);
      root.x0 = h / 2;
      root.y0 = 0;
      root.children.forEach(collapse);
      update(root);  
  }
  
  function collapse(d) {
      if (d.children) {
        d._children = d.children;
        d._children.forEach(collapse);
        d.children = null;
      }
   };
  
  // 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);
  }
  
  function update(source) {
  
    // Compute the new tree layout.
    var nodes = tree.nodes(root).reverse();
  
    // Normalize for fixed-depth.
    nodes.forEach(function(d) { d.y = d.depth * 180; });
  
    // Update the nodes…
    var node = vis.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"; })
      .on('mouseover', function(d, i){
          var dataset = [1,2,3,4]                                    // HERE
          vis.selectAll("line")                                      // HERE
              .data(dataset)                                 // HERE
              .enter()                                       // HERE
              .append("line")                                // HERE
              .attr("x1", this.x)                            // HERE'S THE PROBLEM FOR PERRY
              .attr("y1", this.y)                            // HERE'S THE PROBLEM FOR PERRY
              .attr("x2", 500)                               // HERE
              .attr("y2", 500)                               // HERE
              .style("stroke", "rgb(6,120,155)");}           // HERE
         ); 
  
    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 = vis.selectAll("path.link")
        .data(tree.links(nodes), 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()
        .duration(duration)
        .attr("d", diagonal);
  
    // 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;
    });
  
  };
  
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  </code></pre>