title: difference between d3.event.x and d3.event.pageX
body: <p>I am using mouse event to capture the area selected.</p>
  
  <pre><code>  displayGraph(d3.event);
  
    function displayGraph(event){
    var x=event.x;
    var y=event.y;
    //var x = event.pageX;
   .........................
    rect.x = x;
    rect.y = y;
  ....................
  }
  </code></pre>
  
  <p>In Firefox, event.x is returning undefined. However it works fine in chrome. When i replace event.x with event.pageX and y with event.pageY it works in both browsers.</p>
  
  <p>What is the difference between event.x and event.pageX. why is it showing as undefined in firefox. Is it not supported in firefox.</p>