In Chrome, you can find it on the View menu > Developer > Show Developer Tools.
Then open the Sources tab, and click the pause button icon which is shown in my screenshot. It has three states: grey means inactive, purple means stop on "uncaught exceptions" and blue means "stop on all exceptions".
Click it until it's blue, then reload the page. The Sources tab will show that code exception has stopped when there is an exception. You might well see some spurious errors which are part of the normal execution, just click the play button to carry on. When you get to the exception in your tag, you should see in the variables panel a message describing the error.