For example, when writing frontend code using Angular.js, you sometimes get an error: " <controller name> is not a function: got undefined". Hmm. Well, this controller certainly exists. For the sake of the argument, let's give it the very boring name
MyCtrl. You do the sanity check: is it being included in the HTML page? Yes, it is. What could it be, then? Does the controller have a syntax error in it? You run it through JSLint. No, the syntax seems to be OK.