title: Why d3js exit().remove() don't work?
body: <p>I'm new to d3js, in my understanding.</p>
  
  <pre><code>// links is an array and id is unique key
  var pathData = paths.data(links, function(d) {return d.id;});
  
  pathData.enter().append('').attr() ...
  
  // in there will be delete all the duplicate items
  pathData.exit().remove();
  </code></pre>
  
  <p>But in my code, it recreate a node.</p>
  
  <p>Here is my full code <a href="http://jsfiddle.net/yunfanyunfan/URpfB/34/" rel="noreferrer">http://jsfiddle.net/yunfanyunfan/URpfB/34/</a></p>
  
  <p>click the line, will appear many lines, because the duplicate node not removes.</p>