title: Behavior of events, and the $event variable in Vue.js
body: <p>With the following method "updateCoords", it is necessary to provide the 'event' argument.  The following div tracks the mousemove event and updates the cursors x and y coordinates in real time via methods.</p>
  
  <pre><code>&lt;div id="content"&gt;
    &lt;div @mousemove="updateCoords($event)" style="height:400px;width:400px;border:2px solid black;"&gt;
      {{x}} {{y}}
    &lt;/div&gt;
  &lt;/div&gt;
  
  &lt;script&gt;
    new Vue({
      el: '#content',
      data: {
        x: 0,
        y: 0
      },
      methods: {
        updateCoords: function(event){
        this.x = event.clientX;
        this.y = event.clientY;
       }
      }
    })
  &lt;/script&gt;
  </code></pre>
  
  <p>This function does not work if event is not passed.  It makes sense to me that we would pass something here since X and Y coordinates are dependent on the last location of the event.  But how is this data stored?  Do events track and store data within themselves? </p>
  
  <p>Also it seems to make no difference if I pass my method the special $event variable or not.  Calling...</p>
  
  <pre><code>  @mousemove="updateCoords($event)"
  //is the same as 
    @mousemove="updateCoords()"
  </code></pre>
  
  <p>Does view automatically know that an incoming event argument is $event?  Or is $event important to use in some other particular case??</p>