The Tor Browser / file revision

 const Cc = Components.classes;

 const Ci = Components.interfaces;

 var timer;

 // This test XPConnect's ability to deal with a certain type of exception. In

 // particular, bug 641378 meant that if an exception had both 'message' and

 // 'result' properties, then it wouldn't successfully read the 'result' field

 // out of the exception (and sometimes crash).

 //

 // In order to make the test not fail completely on a negative result, we use

 // a timer. The first time through the timer, we throw our special exception.

 // Then, the second time through, we can test to see if XPConnect properly

 // dealt with our exception.

 var exception = {

   message: "oops, something failed!",

   tries: 0,

   get result() {

     ++this.tries;

     return 3;

   }

 };

 var callback = {

   tries: 0,

   notify: function (timer) {

     if (++this.tries === 1)

       throw exception;

     try {

         do_check_true(exception.tries >= 1);

     } finally {

         timer.cancel();

         timer = null;

         do_test_finished();

     }

   }

 };

 function run_test() {

   do_test_pending();

   timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);

   timer.initWithCallback(callback, 0, timer.TYPE_REPEATING_SLACK);

 }