title: Backbone.js focus event fires two events focus and focusin
body: <p>The view part of my code using Backbone.js is something like this:</p>
  
  <pre><code>var myView = Backbone.View.extend({
  
      events: {
          'focus .cell input'     : "updateCurrentCell"
      },
      updateCurrentCell: function(event) {
          console.log('updateCurrentCell called');
          // Update the current cell.
      }
  }
  </code></pre>
  
  <p>Whenever the input element gets focus, the function is called twice. I tried printing the stack trace using <code>console.trace()</code>. It shows that once the function call originated from <strong>focus</strong> event while the next time from <strong>focusin</strong>.</p>
  
  <p>My attempts to find out how to prevent one of these events getting fired lead me nowhere.
  How can I fix this?</p>