title: When tracking which elements were clicked e.target.id is sometimes empty
body: <p>I am trying to test the following JavaScript code, which is meant to keep track of the timing of user responses on a multiple choice survey: </p>
  
  <pre><code>document.onclick = function(e) {
  
      var event = e || window.event;    
      var target = e.target || e.srcElement;
  
      //time tracking 
      var ClickTrackDate = new Date;
      var ClickData = ""; 
      ClickData = target.id + "=" + ClickTrackDate.getUTCHours() + ":" + 
          ClickTrackDate.getUTCMinutes() + ":" +
          ClickTrackDate.getUTCSeconds() +";";
  
      document.getElementById("txtTest").value += ClickData;
      alert(target.id); // for testing
  }
  </code></pre>
  
  <p>Usually target.id equals to the the id of the clicked element, as you would expect, but sometimes target.id is empty, seemingly at random, any ideas?</p>