Ahhh, JavaScript error messages.

<sarcasm>
They are the epitome of the user friendly error message. Developers love them, because they always tell you exactly where the problem is. Absolute error message perfection.
</sarcasm>

Below is an example of one of these messages that a friend sent:

Nice, eh?

You can tell EXACTLY what the problem is. That... thing... is null or not an object! And we've even got a line number, too!

NOTE: The above message was generated by a script I wrote a while back that is kicked off by the window.onerror event that fires when JavaScript exceptions are thrown. It posts to an application which then emails the developers in question.