title: Updating text link URL in d3
body: <p>I am trying to implement a link in the tooltip of a line chart in d3. 
  Similar to <a href="https://bl.ocks.org/mbostock/3902569" rel="nofollow">this</a>.</p>
  
  <p>The link will be an attribute of the data so I want to be able to change the link, as the tooltip focuses over different parts of the data.</p>
  
  <p>I am not using a div because I want to have a responsive page, and don't want to use absolute positioning.</p>
  
  <p>I can't figure out how to change the link after it had been set.
  So, far I have just tried calling:</p>
  
  <pre><code>  .attr("xlink:href", 'http://www.yahoo.com') 
  </code></pre>
  
  <p>a second time, but this does not update it.</p>
  
  <p>A jsfiddle example is <a href="https://jsfiddle.net/fLrf9okb/" rel="nofollow">here</a>.</p>
  
  <p>Thanks for any help.</p>