Stop suppressing JavaScript errors

Well, despite your impression, jQuery itself doesn't do anything to "suppress" error messages. Now, Firefox does tend to throw away certain kinds of exceptions, notably like what you describe. I often find that wrapping a whole Javascript block in a try ... catch with an alert call should an exception happen is a useful way to deal with it, but it's still irritating.

I am having the same problem in FF 18. I am using JSF and JQuery, though it happens even for plain JS code on the page. I intentionally put javascript code that should throw a syntax error without a word in Firebug. FF 18 has its own built-in console that looks similar to firebug. When I disabled the firebug plug-in the console.log messages started showing up. However, the errors are still not showing up. I just tried Chrome and the errors do appear there.

I've run into this problem several times. It's quite inconsistent and hard to replicate, sometimes it seems related to version issues. Settings rarely seem to make a difference, though "Break on next" sometimes (not always) identifies errors that otherwise slip through.

One thing I've noticed is, it tends to happen for code that is triggered inside a callback function, e.g. from a UI event or from an AJAX call. Sometimes Firefox / Firebug will behave like other browsers and show errors in the console, sometimes it gives nothing at all even for incredibly clear-cut cases like:

console.log('something'); // Shows up in console fine
fail  // Other browsers give undefined variable error, Firefox gives nothing
console.log('something else'); // Never reached, so silent error clearly happens

The best approach I've found to this is:

• Once you've found a no-show error, work back using console.trace() until you reach a point where inside a function, the error is hidden, outside, it shows, adding some code snippet like:

   console.trace();
   fail // cause the error, look out for a trace followed by nothing
  

• If it's an AJAX call, manually add a basic error handler, because for some reason Firefox/Firebug is losing the default:

   $.ajax({
     error: function(a,b,c){
       throw c;
     }, 
     other: '...settings'
   }
  

  • If it's something you can't add an error handling function to, wrap it in a try... catch, for example:

   try {
     // whatever the code is within which there are no errors
   } catch( err ){
     throw err;
   }
  

This should be enough to catch all errors where-ever they are within the scope where Firefox is losing them. Beware of cases where you have a callback within a callback though, you might need to do this twice...