Put random text in window.alert() where ever I got error in JavaScript code. Random text like 1) If you see this, you are fucked; 2) error 001; 3)why today; 4) the code is breaking here etc.

And never removed them. They are the running in production till now. I am just thankful to the gods that the code Nevers break and the user does not get browser alert and also the fact that I don't work there anymore.