title: Why does this syntax work over the other one with d3.json requests?
body: <p>I don't understand why all the examples i find work with json requests like this:</p>
  
  <pre><code>d3.json("file.json", function(data){
     ..do something with data
  });
  </code></pre>
  
  <p>..but when I had to implement it I had to use:</p>
  
  <pre><code>d3.json( "file.json", function(data){}).then(function(data){
      ..do something with data
  )};
  </code></pre>
  
  <p>What is happening there? 
  I'm running a live-server with node.</p>